air exerts pressure in downward direction experiment

If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

To log in and use all the features of Khan Academy, please enable JavaScript in your browser.

Bridge Course Class 7th Science

Course: bridge course class 7th science   >   unit 5.

• Activity: Air is a mixture of gases
• Explanation: Air is a mixture of gases
• Activity: Air exerts pressure

Explanation: Air exerts pressure

• Activity: Air occupies space
• Explanation: Air occupies space
• Activity: Air is present around us
• Explanation: Air is present around us
• Properties and Composition of Air
• Use of Air in Daily Life
• Utility of Ozone Layer

Want to join the conversation?

Video transcript.

Activity Length

10 activities, matter weather, activity type.

In these activities students explore the impressive force of air and learn how air pressure affects their daily lives.

We may not realize it, and we can't always feel it with our senses, the air that surrounds us is exerting a huge amount of pressure on every square centimetre of our bodies.

At this very moment, we have the equivalent weight of a car pushing down on our heads. Do you see anything?

List of Activities :

A ir Pressure Game Egg in a Bottle Balloon in a Bottle What's in a Bottle? The Bernoulli Challenge Bernoulli Candle Experiment Plane Wing Simulator Straw Poppers Human Lung Simulator Build a Barometer Air Cannon Incompressible Water Cup and Card Balloon and Cup Attraction Windbag

Describe the characteristics of air.

Explain how air pressure works.

Discuss how air pressure affects our daily lives.

See individual activities for materials.

We are constantly surrounded by lots of tiny and invisible air particles. We often think of air as being something light and weightless. In reality, air is a gas that takes up space and has mass (weight). Since there is a lot of “empty” space between air molecules, air can be compressed to fit in a smaller volume.

Air not only has mass, but exerts pressure as well. The particles of air push in all directions and the force that is exerted is called air pressure.

While air pressure can refer to the pressure of air within a confined area (car tire or football), atmospheric pressure specifically refers to the air pressure exerted by the air molecules above a given point in the Earth’s atmosphere. The closer we get to the Earth, the higher the atmospheric pressure due to the weight of air particles above. This is why there is less air pressure at the top of a mountain than at sea level. The weight of air above compresses the air particles near the surface of the Earth, creating a higher density of particles. The tool used to measure atmospheric pressure is called a barometer. You cannot use a barometer to measure the air pressure inside a tire, a football, or an air mattress.

When we jump into a pool, we feel the weight of the water pressing down on us from all directions. This force is known as water pressure. The deeper you sink, the more pressure you will feel. This is because you have the weight of the water on top of you trying to compress you.

To help us visualize air pressure, imagine that we’re living at the bottom of an ocean of air. At sea level, the air pressure is greater than on the top of a mountain since you have the weight of more air pushing down on you.

How heavy is that air? A cube of air 1 metre per side has a mass of 1 kilogram. The Earth’s atmosphere is about 480 kilometres thick. This means that on the surface of the Earth, we have 480 kilometres of air pushing down on us. That’s 1,700 kilograms on each of our heads (which is roughly the equivalent of the weight of a male hippopotamus!).

So why don’t we get flattened by all that air pressure? We have air and fluids inside your body that exert a pressure outward, cancelling out the atmospheric pressure around us. This ensures that our bodies do not collapse under the weight of the air around us.

One of the most important concepts to remember in this unit is that air always flows from a place with high pressure to a place with low pressure. Air will perform amazing feats to get from a high-pressure region to a low-pressure region, including pushing and lifting things in its way. Air flowing from a high-pressure region to a low-pressure region is often felt as wind.

To help students remember the direction of airflow, they can use the phrase “winds blow from high to low.”

In these activities, students will discover how changes in air pressure contribute to many different things, including weather patterns, our respiratory system, and the lift required by airplanes.

Air pressure – The force of air particles against a surface. Atmospheric pressure – The air pressure of the Earth’s atmosphere by the air above a given point. Bernoulli’s principle – The faster a fluid (air) flows, the less pressure it creates. Compression – To squeeze together. Density – The mass per unit volume (or the number of air particles in a particular location). Diaphragm – A thin, circular sheet of muscle below the ribcage that contracts and expands to increase and decrease the volume in the chest cavity. Exhalation – The removal of air from the lungs. Expansion – To spread out. Force – A push or pull that can cause an object with mass to change its velocity, direction, or shape. Inhalation – The intake of air into the lungs. Lift – The upward motion generated under the wings as a plane moves forward. Respiratory system – The part of our bodies that allow us to breathe (consisting of lungs, airways, and muscles). Volume – The amount of space occupied by a substance. Wind – The flow of air from a high pressure system to a low pressure system.

Other Resources

NASA | 10 Interesting Things About Air

Science World | YouTube | The Air Show

How Stuff Works | Ears and Diving

Science Kids at Home | Air pressure and Temperature

Kids Science Experiments | Air Pressure

NASA | What makes a plane go up?

Smithsonian National Air and Space Museum | How things Fly

About the sticker

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Time-Travel T-Rex

Related Resources

Discovering a way for people to take flight is undoubtedly one of the most awe-inspiring feats of human ingenuity…, weather is an important part of our lives and one that we cannot control. instead, it often controls how and where…, what happens when a bat hits a baseball why does a rolling ball eventually stop how do we…, related school offerings.

Visit Eureka! Gallery

We believe that now, more than ever, the world needs people who care about science. help us fund the future and next generation of problem solvers, wonder seekers, world changers and nerds..

• Air Exerts Pressure

Don’t we all just love bubble wrap? Isn’t fun to pop those bubbles? But how is it possible? What is actually happening when you’re popping a bubblewrap? Well, it’s simple! When you pop bubble wrap, the air inside the bubble exerts pressure and hence it pops. Interesting isn’t it? Let us study more in-depth about how air exerts pressure.

Suggested Videos

The envelope of air surrounding the earth is called atmosphere . Air has weight. The weight of air presses our bodies all the time . This weight of air acting on a surface causes air pressure . Air pressure can be understood with the help of certain activities.

Browse more Topics under Winds Storms And Cyclones

• Air Expands on Heating
• Thunderstorms and Cyclones
• Materials Required: tumbler, water, square cardboard piece
• Method: Fill up the tumbler with water up to the brim. Cover it with cardboard piece and turn the glass upside down. Slowly remove your hand.
• Observation: Cardboard does not fall and water stays in the glass.
• Inference: air pushes the cardboard up and prevents it from falling.

Activity II

• Materials Required: plastic bottle with cap, hot water, cold water
• Method: Pour hot water into the plastic bottle. Empty the bottle and put the cap tightly. Pour some ice-cold water on it.

• Observation: The bottle will get de-shaped.
• Inference : The air from the bottle expands as it becomes hot. When it is cooled, air contracts. The outside air has more pressure and it crushes the bottle.

Some daily life experiences that show that air exerts pressure

• You find it easier to row the boat when the wind is blowing behind you.
• The wind coming from the back help in flying kite.
• When we suck from the straw, the liquid rises in it.
• The medicine enters the syringe when a piston is pushed out.

High-speed winds are accompanied by reduced air pressure. Let us now perform certain experiments that will show that high-speed winds reduce the air pressure.

Activity III

• Materials Required: Two balloons
• Method: Blow the balloons and tie string to it. Hang them 10 – 12 cm apart on a rim. Blow air in between the balloons.

• Observation: The balloons will move closer.
• Inference : The air pressure between the balloons is reduced due to more speed. Air moves from higher pressure to lower pressure bringing the balloons closer.

Activity IV

• Materials Required: Bottle, crumpled piece of paper
• Method: Crumple a small piece of paper into a ball of a size smaller than the mouth of an empty bottle. Hold the empty bottle on its side and place the paper ball just inside its mouth. Now try to blow on the ball to force it into the bottle.

• Observation: The paper does not move inside.
• Inference : The air pressure at the mouth of the bottle is reduced due to more speed. This forces the air out from the bottle. This prevents the crumpled paper ball to move inside.

Question For You

Q1. Give Reason – Why is the roof of houses blown off when a strong wind is blowing?

Ans: The strong wind above the roof lowers down the air pressure just above the roof. This forces the air from the air to move outward blowing off the roof of the house.

Q2. A child blows air with a straw near the opening of another straw which has its other end in a soft drink bottle. What do you think will happen and why?

Ans: The level of soft drink will rise in the bottle. This will happen because the air pressure is reduced above the straw hence the drink will rise in it.  

Customize your course in 30 seconds

Which class are you in.

Winds, Storms and Cyclones

2 responses to “thunderstorms and cyclones”.

I have to make project on cyclone family a disaster it’s very little I need more 15 pages If u can so please help me doing my project

I wanna write on “All the Topics” ,So try to provide all of it

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Download the App

• Skip to primary navigation
• Skip to main content
• Skip to primary sidebar

• FREE Experiments
• Kitchen Science
• Climate Change
• Egg Experiments
• Fairy Tale Science
• Edible Science
• Human Health
• Inspirational Women
• Forces and Motion
• Science Fair Projects
• STEM Challenges
• Science Sparks Books
• Contact Science Sparks
• Science Resources for Home and School

Air Pressure Demonstration – Drinks Dispenser

February 24, 2019 By Emma Vanstone Leave a Comment

This easy activity is super simple and great for learning about air pressure with a practical use as well!

What is air pressure?

Air and its particles are crashing into us all the time. What we call air pressure is the force of these particles hitting a surface.

When you suck a straw you reduce the pressure inside the straw, making the pressure outside the straw acting on the liquid greater than the pressure inside the straw. This pushes the liquid up the straw, allowing you to drink it!

For this air pressure experiment you’ll need

Peg – optional, but helpful

Plastic bottle – I used a 750ml bottle

Plasticine or putty

Plastic Straw

Small container

How to make an air pressure drinks dispenser

Carefully make a small hole about half way up the bottle and push the straw through the bottle leaving ⅓ to ½ on the outside.

Fill the bottle about three quarters full of water.

Blow up the balloon, twist and seal the neck with a peg. Carefully place the end of the balloon on the bottle neck and place a glass under the straw.

When you’re ready remove the peg and watch as the water shoots out of the straw into the glass!

Be careful as it might shoot out further than you expect.

Why does this happen?

Air presses down equally on the water in the bottle and in the straw when there is no balloon present ( or the balloon is pegged ) but when the peg is removed, air from the balloon increases the air pressure in the bottle which pushes down on the water, forcing it through the straw.

More Air Pressure Experiments

Demonstrate the Bernoulli Principle with this easy demonstration using a plastic bottle and ball of paper.

Suck a boiled egg into a jar without touching it.

Build and launch a bottle rocket !

Last Updated on November 18, 2021 by Emma Vanstone

Safety Notice

Science Sparks ( Wild Sparks Enterprises Ltd ) are not liable for the actions of activity of any person who uses the information in this resource or in any of the suggested further resources. Science Sparks assume no liability with regard to injuries or damage to property that may occur as a result of using the information and carrying out the practical activities contained in this resource or in any of the suggested further resources.

These activities are designed to be carried out by children working with a parent, guardian or other appropriate adult. The adult involved is fully responsible for ensuring that the activities are carried out safely.

Reader Interactions

Leave a reply cancel reply.

Your email address will not be published. Required fields are marked *

• Activities for Kids
• Family Life

Under Pressure! 10 At-Home Science Experiments That Harness Air

If the at-home orders have you scrambling for indoor activities , we’ve got easy science experiments you can pull out at a moment’s notice from the comfort of your home. Each kids science experiment reveals air’s invisible power, and (usually) uses what you’ve got in the recycling bin to demonstrate it. Read on to learn how to levitate water, submerge tissues without getting them wet and suck an egg into a jug using only a match.

Keep it Simple

Thankfully, science experiments don't have to be super complex or time consuming. These easy-peasy experiments only require a little prep and leave a big impression on tiny minds. Plus, we’re betting most of what you need to test these theories is already lying around your house.

1. Sink or Swim. Instead of bobbing for apples, your tiny tot will make straws dive and surface with a gentle squeeze. The Kids Activities Blog  lays out the important deets for this hands-on experiment that uses a two-liter bottle and play dough to fully certify straws as scuba-ready. Take the dive into serious science with this one!

Why it works: Squeezing the bottle increases the air pressure inside the bottle and forces water up into the straw, which makes it heavy enough to sink.

2. Blow Their Minds . Bet your cutie a clean room that she can’t blow a rolled up piece of paper towel into an empty bottle. Sounds like a safe bet, right? But thanks to air pressure, the cards are definitely stacked in your favor. To set up the experiment, place an empty two-liter bottle on its side. Ball up the corner of a paper towel that’s about half the size of the bottle’s top and place it just inside the opening then challenge your little scientist to blow the paper towel into the bottle (Trust us, it can’t be done). No matter how hard she tries, she’s not going to win that bet. Learning plus a clean room? We’ll take it!

Why it works: Even though you can’t see it, that bottle is full of air; when you try to blow something into it, there’s just no room.

3. Be Unpredictable. Two balloons, a yardstick, string, and a hairdryer are all you need for this experiment that will keep your mini me guessing. To get things moving in the right direction, blow up the balloons to the same size and then use the string to attach them, a few inches apart, to the yardstick. Once you’re all set up, ask your kidlet what will happen to the balloons when you aim air from the hair dryer between the two balloons. The obvious answer? They’ll be blown apart. But once your wee one takes aim, she’ll see that the balloons are actually pushed together rather than apart. Who knew?

Why it works: Blowing air between the balloons lowers the air pressure and makes the pressure surrounding them higher, pushing them together.

4. Levitate Water . You won’t need to incant Wingardium Leviosa with perfect pronunciation to suspend water during this exciting experiment. Start by filling a glass of water about 1/3 full, then cover it with a piece of cardstock. Tip the glass over, keeping the cardstock in place with your hand, and hold the whole shebang over your unsuspecting kidlet’s head (or a sink if you want to do a test run first!). Then slowly let go of the cardstock while your mini me waits excitedly below. Look ma, no splash! The card stays in place and your little guinea pig stays dry.

Why it works : The outside air pressure working against the cardstock is greater than the weight of the water in the glass.

5. Grab a Tissue. To be wet or not to be wet is the question answered in this simple experiment full of drama. To set the scene, loosely crumple a tissue so that when you stick it in a small glass and turn it over the tissue doesn’t fall out. Then, have your little lab assistant fill a bowl with water, turn the glass over and submerge it completely (psst… keep the glass parallel to the water to make the experiment work). Ta da! The tissue stays dry even when it’s below the water line.

Why it works: The air pressure inside the glass is strong enough to keep the water out and the tissue dry.

Complicate Matters

Get mom or dad in on the action with these experiments that take a little more time and some helping hands to demonstrate just how powerful air pressure can be.

6. Blast Off. Nothing makes air pressure more tangible than a classic bottle rocket  launched on a sunny summer afternoon. You and your sidekick can spend time fashioning a plastic bottle into a space-worthy vessel with a cone top and flamboyant fins on the side. Then, hook it up to the air pump and let her rip! Up, up and away! Science Sparks has simple instructions you can use (and even a cool video!) to make one with your budding scientist.

Why it works: Pumping air into the bottle builds up pressure until you just can’t add any more and all that force sends the rocket flying.

7. Make Eggs Magical. This “look ma, no hands, wires or mirrors” trick will get them every time; an egg being sucked into a jar while your little scientist delightedly looks on is always a hit. To perform this illusory feat, you’ll need a glass jar with an opening just smaller than an egg (think: old school milk jug) and a peeled, boiled egg. When you and your Little have checked these items off your list, it’s time to start the show. Mom or dad should toss a lit match into the glass jar, followed by your mini lab assistant, who’ll quickly set the egg over the opening. Abracadabra! Alakazam! The match dies out; the egg gets (seemingly) inexplicably sucked into the bottle. And just like that you’ve performed another bit of parent magic without breaking a sweat.

Why it works: The match uses up the air inside the bottle. Once that happens the pressure outside the bottle is greater and pushes the egg down into the bottle.

8. Build a Barometer. The invisible air pressure around us is always changing, but try explaining that to the tot lot. We've found a seeing-is-believing DIY barometer experiment to turn the tides for your tiny skeptic. Not only will you reveal ever-changing air pressure, but you can also predict any summer storms heading your way. Get all you need to know about making your own version using a screw-top jar, rubber bands and a straw at Wonderful Engineering .

Why it works: When the air pressure is high, it pushes down on the straw tilting it up, and when it’s low, pressure inside the jar pushes up against the straw pointing it down.

9. Inflate Marshmallows. Put those marshmallows you’re stockpiling for summer s’mores to good use in this DIY vacuum experiment. To make the vacuum, use a hammer and nail to pierce a hole (big enough to fit a straw) into the lid of a screw-top glass jar. Next, stick a straw ever-so-slightly into the hole and seal the edges with play dough or molding clay so there’s no way for the air to get out other than through that straw. Now you’re ready to see what happens to a marshmallow when it’s trapped inside; place the marshmallow in the jar, screw the top back on, and have your mini me take the air out gulp by gulp through the straw (just be sure to cover the straw hole between breaths so no air makes it back in). As the air is removed, the marshmallow expands, like a nightmare vision straight out of Ghostbusters . Who you gonna call?

Why it works : When you use a straw to remove all the air from the jar, there’s no air left working against the marshmallow. Instead, the air trapped inside the marshmallow is able to expand.

10. Pit Balloons Against Bottles. Is your future scientist ready for another challenge? Just like blowing a paper towel into a jug, this science experiment from Steve Spangler Science  is oh-so-much harder than it looks. To entice your little experimenter, place an un-inflated balloon into an empty plastic bottle and ask him if he thinks he can blow it up. Easy right? But no matter how hard he tries, that balloon just won’t fill with air! The trick to inflating the balloon  is a simple one that takes mom or dad’s helping hand and just like that, what was once impossible becomes possible!

Why it works: At first, the bottle is full of air so there’s no room for the balloon to expand when you try to blow it up. But when you try this experiment after the trick, there’s an escape route for the air inside the bottle, leaving room for the balloon to inflate.

Need some fresh ideas?

Subscribe to our weekly newsletter for expert parenting tips and simple solutions that make life instantly better.

By subscribing you agree to Tinybeans Terms and Privacy Policy

Related reads

Why Are Gen Z Kids Covering Their Noses in Family Photos?

Screen Time for Babies Linked to Sensory Differences in Toddlerhood, Study Shows

Kids Shouldn’t Have to Finish Dinner to Get Dessert, Dietitian Explains

The Questions Parents Should Be Asking Their Pediatrician—but Aren’t

6 Better Phrases to Say Instead of ‘Be Careful’ When Kids Are Taking Risks

• your daily dose

• and connection

• Your daily dose

• ASME Foundation
• Sections & Divisions
• Sign In/Create Account

5 Ways to Demonstrate Air Pressure to Children

• Topics & Resources

Date Published:

Nov 22, 2010

Aurora Lipper

This story was updated on 10/11/2022.

Note: when conducting at-home science experiments with children, an adult should always be present. Even the simplest experiments have the potential to go wrong.

The ordinary pressure of the air surrounding us is 14.7 pounds per square inch—but this can change based on a few factors, such as when the wind blows or a car or airplane accelerates. Wherever the air pressure is higher, there will be a stronger force or push against an object. Similarly, when an air particle speeds up, it actually “pushes” less.

Imagine that fast-moving air particles are in so much of a hurry that they don’t have time to apply force—this is the principle used to make airplanes fly. When a plane moves along the runway, the air above the wing speeds up, lowering the pressure so that the air below the wing can push the plane upward.

Interested in testing out these principles in a more tangible way? Try one or more of the following experiments:

Water Glass Trick

Step 1: Fill a cup one-third with water.

Step 2: Cover the entire mouth of the cup with an index card.

Step 3: Holding the card in place, take the cup to the sink and turn it upside down.

Step 4: Remove your hand from underneath.

Voilà! Because the water inside the cup is lighter than the air outside, the card is held in place. This is due to about 15 pounds of force from the air pushing up, while the force of the water pushing down is only about one pound of force.

Fountain Bottle

Step 1: Fill a 2-liter soda bottle half full of water.

Step 2: Take a long straw and insert it into the mouth of the bottle.

Step 3: Wrap a lump of clay around the straw to form a seal.

Step 4: Blow hard into the straw—then stand back.

When you blow into the straw, you’re increasing the air pressure inside the sealed bottle. This higher pressure pushes on the water, forcing it up and out of the straw.

Ping-Pong Funnel

Step 1: Put a ping-pong ball inside the wide part of a funnel.

Step 2: Blow hard into the narrow end of the funnel.

Step 3: You’ll notice that the ball doesn’t pop out of the funnel—but why?

This is because as you blow into the funnel, the air moves faster and lowers the air pressure underneath the ball. Because the air pressure is higher above the ball than below it, it’s pushed down into the funnel—no matter how hard you blow or in which direction you point the funnel.

The Million Dollar Bet

Step 1: Place an empty water or soda bottle down horizontally on a table.

Step 2: Roll a piece of paper towel into a small ball about half the size of the bottle opening.

Step 3: Tell a friend you’ll pay them one million dollars if they can blow the ball into the bottle.

Don’t worry about losing money—because this is impossible. No matter how hard someone tries to force more air into the bottle, there's no room for it. The air will flow right out, pushing away the paper ball.

Kissing Balloons

Step 1: Blow up two balloons and attach a piece of string to each.

Step 2: Place one balloon in each hand, holding them by the string.

Step 3: Position the two balloons so they are at your nose level and six inches apart.

Step 4: Blow hard into the space between the balloons.

As you lower the air pressure in that space between the balloons, the pressure of the surrounding air becomes higher. This automatically pushes the balloons together, causing them to “kiss.”

[Adapted from “Top Ten Air Pressure Experiments to Mystify Your Kids-Using Stuff From Around the House,” by Aurora Lipper, for Mechanical Engineering , January 2008.] Read More: How to Mentor Young Engineers Experiential Learning and Cooperative Education Pay Off Engineering Education, Family Style

Related Content

ASME Membership (1 year) has been added to your cart.

The price of yearly membership depends on a number of factors, so final price will be calculated during checkout.

You are now leaving ASME.org

CBSE Class Notes Online – Classnotes123

CBSE Class Notes, Worksheets, Question Answers, Diagrams , Definitions , Diffrence between , Maths Concepts, Science Facts Online – Classnotes123

Air And Water – Class 5

Air Around Us 

Air is very important to us. We cannot live without air even for a few minutes. It is all around us, we take it in when we breathe. Air consists of a mixture of gasses like oxygen, nitrogen, helium etc. it also contains bacteria, viruses. The thick layer of air that surrounds the earth is called the atmosphere. Earth’s gravity holds the atmosphere around the Earth. It protects us from the harmful Ultraviolet rays of the Sun.  

The Atmosphere 

The several hundred kilometers thick layer formed by the air around the Earth is called the atmosphere. The density of air decreases with height. Air density is greatest at the surface, and decreases as we move up in the atmosphere because the weight of air above becomes less.  The atmosphere plays a major role in protecting us from meteoroid hits by burning them up in the mesosphere before they can hit the surface of the earth. It also protects us from harmful UV rays. 

5 Important Layers of the Atmosphere 

5 Important layers of atmosphere are :

• The Troposphere
• The Stratosphere

The Mesosphere

• The Thermosphere 
• The Exosphere

The Troposphere : 

• The lowest layer nearest to the Earth’s surface is called the troposphere. 
• It extends upto about 15km above the surface.
• Humans live in the troposphere.
• Most weather changes occur in this layer.
• Clouds are formed in this layer because 99% of the water vapor in the atmosphere is found in the troposphere.
• The Air gets colder as you climb higher in the troposphere.

The Stratosphere:

• The second layer of the atmosphere is called the Stratosphere.
• It extends from the top of the troposphere to about 50km above the surface.
• The ozone layer is found in this layer.
• Unlike the troposphere, the stratosphere actually gets warmer the higher you go.
• Commercial jet planes usually fly in this layer.
• The layer that Lies above the stratosphere is called mesosphere.
• It extends to about 85-90 km about Earth’s surface. 
• Most meteors burn up in this layer.
• Temperatures once again grow colder as you rise up through the mesosphere.

The Thermosphere 

• The layer that Lies above the mesosphere is called the thermosphere.
• It extends to about 500-600 km above Earth’s surface. 
• High-energy X-rays and UV radiation from the Sun are absorbed in the thermosphere.
• The layer of the air is very thin in this layer.
• This layer absorbs High-energy X-rays and UV radiation from the Sun.
• Many satellites orbit Earth within this layer

 The Exosphere

• The layer that Lies above the thermosphere and fades into space is called the exosphere .
• It extends somewhere between 100,000 km and 190,000 km above the surface of Earth. 

The Importance of the Atmosphere

• It contains oxygen , which all living organisms need to survive.
• It has carbon dioxide which is needed by the plants for the process of photosynthesis.
• Air is needed for burning as it contains oxygen which helps in combustion.
• It has a layer of gas called the ozone layer which is present in the strastopsphre which protects us from harmful UV rays of the Sun thus protecting us from many skin diseases and eye problems.
• Gasses present in the atmosphere  reflect or absorb the strongest rays of sunlight. 
• It also moderates the Earth’s temperature.
• Atmosphere also protects us from meteoroids.  

What does Air Contain 

The air around us is a mixture of several gasses. It contains 78% nitrogen, 21% oxygen and 1% mainly argon and 0.03% carbon dioxide. In addition to these gases, air also contains some amount of water vapor, dust and smoke. Germs are also present in the air. 

Oxygen: 

• Oxygen is the most important gas needed for the survival of all living organisms. 
• Oxygen forms ⅕ th of the Earth’s atmosphere. 
• It is one of the main elements that is present in the air. 
• Nitrogen is the most abundant element on our planet.
• It has two molecules of nitrogen. 
• Plants use nitrogen with the help of bacteria present in the soil.
• Animals get nitrogen from plants, fish and meat.

Carbon Dioxide : 

• It is a colorless, odorless gas present in the atmosphere which is important for the plants for the process of photosynthesis.
• It is an important greenhouse gas which helps to trap heat in the atmosphere. 

Other Gasses:

• Some percentage of other gasses like hydrogen, helium, neon, argon and krypton are also present in the air.
• Argon is a colorless and odorless gas present in air. It is used in making light bulbs and fluorescent tubes.  

Water Vapour : 

• Water vapour is the source of moisture for clouds, rain and frost.
• It is formed because of evaporation of water from the surface of water bodies.
• The amount of water vapour present in the air is called humidity. 
• Water vapour absorbs heat in the lower atmosphere and radiates the heat in all directions. 

Air is everywhere around us. We are not able to see the air but it is present everywhere from an empty cup to  an empty room. 

Experiment to prove that air occupies air

Take a balloon and blow air into it.

You will notice that the size of the balloon increases.

This shows that air takes up space. 

Air Has weight

Even though we cannot feel it, air has some weight.

Anything with mass has weight and air has mass because we can feel it when the wind blows.  

Experiment to prove that Air has weight 

• Take two balloons (green and red ). 
• Fill the two balloons with equal amounts of air. 
• Tie each balloon at the ends of the stick or hanger  respectively.
• Now deflate the red balloon.
• The green balloon will drop down as the stick will tilt down towards the air filled balloon because of the weight of the air inside it. 

Air Exerts Pressure

Air pressure is the force with which air pushes against the Earth’s surface. Air has density and mass. Due to its mass it puts pressure on the things around it. 

 Experiment to Prove that air exerts Pressure  

•    Take a glass of water and fill it completely with water. 
• Cover the mouth of the glass with cardboard making sure there are no bubbles in the water below the cardboard.
• Now press the cardboard with your hand and invert the glass and remove your hand from the cardboard.
• The cardboard will not fall as the air exerts pressure on the card to keep it in place.

Air Exerts Pressure in the upward direction

Experiment to prove air exerts pressure in the upward direction .

• Take a glass of water and fill it with water to the brim
• Cover the tumbler with a stiff paper.
• Press the paper with your hand and turn it upside down. 
• We will see that the paper will not fall and water stays in the glass.
• The air pushes the paper up,i.e, exerts pressure in the upward direction preventing it from falling. 

Air Exerts pressure in Downward direction

Experiment to prove air exerts pressure in downward direction.

• Take a plastic bottle filled with water and close the cap tightly .
• With the help of a pin make a hole on the side of the bottle.
•   We will see that the water will not come out of the hole.
• Now open the cap of the bottle . 
• We will see that the water will come out of the hole because air exerts pressure in a downward direction. 

Air is needed for burning

 experiment to prove that air is needed needed for burning .

• Take a candle and light it.
• The candle will continue to burn due to the air present around it . 
• Cover the candle with a lid now . 
• After sometime we will see that the candle will stop burning.
• This proves that air is needed for burning as gasses like oxygen present in air helps in combustion. 

Atmospheric pollution 

• Air contains particles of dust, smoke and harmful gasses. They are called atmospheric pollutants as they make the air dirty and polluted. 
• Atmospheric pollutants are substances that accumulate in the air to a degree that is harmful to living organisms or to materials exposed to the air. 
• Atmospheric pollution is a big threat which leads to a number of diseases.
• Burning of fossil fuels, gasses released by automobiles, factories & industries release smoke and harmful gasses in the air which degrade the quality of the air .
• Atmospheric pollution can lead to the occurence of a number of respiratory disorders and heart diseases among humans.
• It also leads to global warming. 

Water 

About 71% of the Earth’s surface is covered with water. It is found everywhere from oceans to lakes to ground and even in the sky as water vapour. We need water to carry out our daily activities. We cannot imagine our life without water. Rainwater is the main source of water on Earth. 

Uses of water :

• Water is used for agriculture for the purpose of irrigation.
• Water is used for washing clothes, drinking, bathing, cleaning etc.
• It is also used in watering plants.
• Water is used in industries for power generation.
• One of the important uses of water is fire extinction.

Impurities in water:  

Substances such as mud, sand, dirt and germs make water unfit for use. These are called impurities. Impurities are of two types: 

• Soluble impurities : impurities that dissolve in water. E.g: Salt
• Insoluble impurities : impurities that do not dissolve in water. E.g: sand and mud 

A solution is a mixture in which substances are completely dissolved. It can be defined as a special type of mixture where two or more substances are combined in such a way that they evenly spread and mix with each other. 

Example: sugar mixed with water becomes a solution. 

2 Substance to make Solution

The two substances that make a solution are: 

Solute : 

• The substance which is soluble in other substances is called a solute. 
• Solute is the component of the solution which is present in small amounts.

Solvent: 

• a substance in which the solute is dissolved is called a solvent.
• Solvent is the component of solution which is present in large amounts.

Let us take an example to understand about solute and solvent: 

When we mix salt and water it completely dissolves with each other and forms a solution. Here, salt is the solute and water is the solvent. 

Removing Insoluble Impurities 

Different methods are used to remove various soluble and insoluble impurities from water. Some substances like stones, mud,and sand do not dissolve in liquid(say water) and are called insoluble substances. We can separate the insoluble substances from water by sedimentation followed by decantation and filtration. 

Sedimentation and decantation 

when we mix mud in water, the color of the water gets changed. After some time  we will see that the insoluble particles of mud settle down at the bottom. These are called sediments. This process of separating insoluble substances is called sedimentation. 

Sedimentation steps

• Collect impure water containing mud in a beaker.
• Keep the water undisturbed for some time
• After some time, the mud settles down at the bottom of the beaker and is called sediment. 

After the insoluble sediments have settled down, the clear water can be removed into another container. This process is called decantation .  

Filtration: filtration is a process in which water containing insoluble substances are poured into a funnel having a cone of filter paper. Insoluble substances are caught in the filter paper and the clear water passes through it and gets collected in a vessel called a filtrate. This is a better process of separation than sedimentation and decantation. 

Removing Soluble Impurities

It is more difficult to remove soluble impurities than insoluble ones. We can separate soluble substances from water by evaporation  and distillation. 

Boiling: in this process the soluble substances can be separated by heating the water(liquid). When all the water evaporates we will get the substance. Water is lost during the process of boiling. 

Example: sugar and water solution is heated till the water evaporates leaving behind sugar particles.

Distillation: It is a method of purifying water generally performed in laboratories. The water collected after this process is called distilled water. It is free of any impurities. It is used in car batteries and medicines.

Drinking water

For a healthy living clean drinking water is to be consumed. Drinking water needs to be purified before consumption because impure water can lead to a variety of diseases.

Three methods are usually used for treatment of water: 

• Screening : screening is a wastewater pre-treatment. In the process of screening the water is taken from lakes, rivers and passed through screens that remove large impurities like stones, leaves, plastics etc. 
• Sedimentation: It is a process that removes solids that float and settle in the water. Water is collected in large tanks and left undisturbed for a few days. The heavier impurities settle down at the bottom. This waste is removed periodically. Chemicals like alum are added to purify water. 
• Filtration: after the process of sedimentation, the water is filtered through sand beds to filter out small insoluble particles. 
• Chlorination : Next, chlorine is added in small amounts to disinfect the water . The water is now safe for drinking. 

Methods of purifying water at home – to make it fit for drinking

• Boil the water for about 15 mins to kill the germs and filter it.
• Add water purification or disinfecting tablets like chlorine dioxide in water to filter water.
• Use a water filter to store drinking water.
• Add potassium permanganate crystals in wells to clean water. 
• Small amount of bleach can be used to clean water. 

Related Posts

About Jaishree Gorane

3 comments on “air and water – class 5”.

These types of websites are really helpful . I really love this, Good job 👍

Extremely good.

Thanks Jasneet

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Save my name, email, and website in this browser for the next time I comment.

How to do an Air Pressure on Water Experiment for Kids

• September 26, 2021
• 5-6 Year Olds , 7-9 Year Olds , Physics

Have you ever wondered how water can be pulled up into a straw? Or what happens to the air pressure when you go up in an airplane?

Now, you can explore these questions with this awesome experiment. The science behind this phenomenon is air pressure.

If you have ever had a bike pump, then you know that the higher the pressure inside, the more forcefully it can push air out . This same principle also applies to water being sucked up through your water dispenser.

Air Pressure and Water Experiment Supplies

Air Pressure on Water Experiment is an awesome physical science experiment as it can be done using simple and easily available supplies. Here is the list of items you need to collect before you start the experiment.

1) A Balloon

2) A Plastic straw

4) A small container (glass one is better to get a good visual experience) or a Peg

5) Putty or Plasticine

6) A Plastic water bottle (Make sure it is clean and clear no matter the shape and size.)

7) Food Color

8) Some other miscellaneous things like kids-friendly knife, glue, metal scale, etc.

Directions to do Air Pressure on Water Experiment

Step-1: Select a place where you feel free to do experiments with water like sinks or outdoors as this activity messy up things with water.

Step-2: Now, pick an old and clear plastic bottle and make a hole of 10cm at the middle of the bottle. You can use kid-friendly knife or scissors to make hole. Whatever the tool you use, make sure you are moving it clock and anti-clock wise direction to achieve a good round shape. You can also use a soldering rod to make exact size hole as of straw.

Step-3: Once the hole is ready, insert the plastic straw into it and seal any leakages around the hole using hot glue. You can also use putty or plasticine to seal it.

Step-4: Then, take a small container and add some amount of water. Also add a few drops of food color and into the water to make it colourful. This colourful water is good to experiment with as it gives good visual experience of the experiment.

Step-5: As a next step, pour the color water into the plastic bottle fixed with straw up to half way. And keep a peg or small glass or transparent container under the other end of the straw which is hanging outside of the bottle.  

Step-6: In this step, take a medium sized balloon and inflate it using your mouth or any balloon blower machine. Seal the mouth of the inflated balloon and fit it around the mouth of the bottle carefully. At this point, our school science fair project set up to show Air Pressure is ready for demo.

Step-7: Now, release the secured mouth part of inflated balloon such that the air inside it goes straight down into the plastic bottle.

Step-8: You will notice the color water inside the plastic bottle moving out of the straw towards the small container placed beside the plastic bottle under the open end of straw.

What is the science behind the water movement in this experiment?

In this physical science project, the air gives pressure equally on the water and inside straw when there is no balloon around the mouth of the plastic bottle.

But when the inflated balloon is set up on top of the plastic bottle i.e. around its mouth part, the air inside the balloon forces down into it.

Thus, creates increased pressure on the surface of the water and presses the water molecules down due to force and gravity. This increased pressure inside the water pushes water into the straw. And hence the water moves towards the straw and stores in the small container placed outside.

The science concepts learned through this classic Air Pressure Experiment on Water include:

1) Atmospheric Pressure: The pressure applied by the molecules (that has weight) present in the atmosphere or air towards the surface of the Earth due to the force and gravity is known as Atmospheric Pressure. Atmospheric Pressure is also known as Barometric Pressure.

2) Pressure: The amount of force exerted per unit area byt the surrounding surfaces and particles is known as pressure. The pressure unit is pascal. The formula of pressure is P=F/A. Absolute pressure, atmospheric pressure are the types of pressure.

3) Potential Energy: The energy developed due to the pressure or force with in itself is known as potential energy. Potential energy can also use electric charges to build its energy.

In this experiment, the air inside the inflated balloon develops potential energy and tries to come out of it. And hence, the water feels pressure when the mouth of the inflated balloon releases.

This pressure makes the water flow out of the plastic bottle and into the small container placed beside it through the straw.

Other Air Pressure Experiments You Can Try at Home

Balloon and Pin Experiment

Egg in a Bottle – Air Pressure Experiment

Balloon in a Bottle : Air Pressure Experime nt

Drip Drop Bottle-Water Bottle Pressure Experiment

What we learn from Air Pressure on Water Experiment

• Students learn about Air and Atmospheric pressure
• Explore different types of forces, pressures, and potential energy
• Get knowledge on various science terms such as atmospheric pressure, force, pressure, stress, etc.
• Can be a great science fair idea
• Encourages children to actively participate in science work-shops and events

How do you define Air Pressure?

Air pressure is the pressure created by the weight of the particles in the air that are forcing to move down to Earth because of gravity.

In simple words, air around us encompasses of a lot of air molecules (that has weight), which exerts pressure whenever they get in touch of any objects. This is the pressure we call it as Air Pressure.

Air pressure is also known as Atmospheric Pressure. As we use Barometer to generally measure atmospheric pressure, we also call it as Barometric Pressure.

The standard unit of atmospheric pressure is equivalent to 101,325 Pa or 29.9212 inches Hg or 760 mm Hg or 14.696 psi.

P_h= P_0 e^{\frac {-mgh}{kT}}

P_0= sea level pressure

P_h= pressure at height h

g= Acceleration due to gravity

K= Boltzmann’s Constant (Ideal gas constant divided by Avogadro’s number)

T= Absolute Temperature

M= Mass of one air molecule

Safety Measures

1) It is highly recommended to wear safety glasses to protect your eyes.

2) Handle the hot glue or hot melting glue carefully otherwise children may burn their hands

3) Use kid-friendly knife

4) Always there must be an adult supervision while conducting this experiment

When you inflate the balloon, the air inside it creates potential energy and faces pressure against the rubber surface of balloon. And when the inflated balloon placed over the neck of the plastic bottle, the air pressure of balloon flows into it. This creates higher pressure on the top of the plastic bottle and thus creates even more pressure inside water in the bottle. This pressure moves water from the plastic bottle to the container placed beside it through the straw.

There are many ways to demonstrate pressure through our daily activities. Here is the easy one to explore or demonstrate pressure: 1) Take a plastic water bottle and fill it with water to its half way. 2) Place a straw into its neck part and seal the leaky edges using putty or clay. 3) Blow heavily into the straw which creates increased air pressure inside the bottle. 4) This increased pressure inside the bottle pushes the water out of straw like a fountain.

Water dispenser plays important role in restaurants, hotels, offices, etc. And it is the perfect example to demonstrate Air Pressure. Water dispenser is useful to supply normal to moderate to hot water whenever we press button. Water dispenser is a set-up of upside down 4-5 gallon water bottle at the top of the machine. Mostly, water dispensers work by pressing button, through which you are increasing the pressure inside by allowing the air inside the bottle. And that’s the way, you can dispense water from the machine when air allowed inside the bottle.

Air has mass as it contains a lot of tiny particles that possess weight. These particles when touched against any solid object, exerts pressure. The pressure exerted by air molecules in all directions around us, known as air pressure. However, because of the air particles weight, we experience more air pressure when we stay closer to the surface of Earth.

Take one litre plastic bottle and make a straw size hole at the middle of it. Insert a straw through the hole and seal the leakages using clay or putty. Outside the bottle and under the other open end of the straw, place a small container. Now, fill half of the bottle with water and cover its mouth using inflated balloon. When you release the air inside the balloon, there creates high pressure inside the bottle and water. Thus, the water is let outside the bottle through the straw and into the container placed beside the bottle.

Here are some of the situations where we use air pressure in everyday life: 1) When we drink through straw, the air pressure inside it decreases while outside pressure increases and forces the drink to suck inside the straw. 2) Consider a vacuum cleaner, it has a fan inside it which creates low pressure environment inside the machine. Whereas the outside atmospheric pressure forced inside and takes the dirt and air molecules to suck inside the machine. 3) Syringes creates pressure by plunging the nob of it while taking the blood from human body. This pressure sucks the blood from human body into the syringe easily.

1) The pressure of air inside car tires holds the car weight 2) The flight movement up in the sky because of the air pressure on its wings. 3) Bullet firing from the gun using gas pressure. 4) Inflation of balloon because of air pressure developed inside. 5) Sucking a drink through straw using pressure created inside it.

Leave a Reply Cancel Reply

Your email address will not be published. Required fields are marked *

Name  *

Email  *

Add Comment  *

Save my name, email, and website in this browser for the next time I comment.

Post Comment

Stack Exchange Network

Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Q&A for work

Connect and share knowledge within a single location that is structured and easy to search.

Why is air pressure in all directions?

• Here is a typical definition of air pressure:

Air pressure is caused by the weight of the air molecules above. Even tiny air molecules have some weight, and the huge numbers of air molecules that make up the layers of our atmosphere collectively have a great deal of weight, which presses down on whatever is below.

And yet, all sources I've seen state that air pressure is equal in all directions.

1 & 2 seem contradictory.

Related question:

Why does air pressure from above not crush us? The answer I see consistently given is that an equal air pressure from below balances it out. But if a car were resting on me from above and crushing me, then another car pressing against me from below would not relieve that pressure -- it would only increase the pressure I would feel! If I were in an enclosed closet, and one of the walls were to press in against me, and then the opposite wall would also press in against me, the second wall would not "balance" things out, but rather only increase the pressure I would feel!

• mechanical-engineering

• $\begingroup$ Consider the flowing property of pressure in a fluid. Pressure is dependent ONLY on depth of fluid. For example: A 1 ince diameter pipe one mile high has exactly the same pressure at the bottom as a 500 foot diameter pipe of the same height. This isn't an answer, just something you should consider to understand this a little more. $\endgroup$ –  Bassinator Commented Apr 11, 2015 at 15:44
• 1 $\begingroup$ The short answer is that you are confusing a gradient with an anisotropy. Pressures change from one location to another, but not from one orientation to another. Fluids can't support shear without deforming so as to relieve that shear. Without shear along the boundary of a control volume, any net pressure difference would either cause the entire volume to accelerate, or cause it to deform in shape. Both of these result in kinematic energy appearing to account for the work imbalance between the high pressure PV work and the lesser low pressure PV work. $\endgroup$ –  Phil Sweet Commented Sep 27, 2018 at 2:41

8 Answers 8

Why is air pressure equal in all directions?

Imagine what it would mean for a thin flat piece of metal if the pressure were not equal from above and below. There would be more pressure pushing down from the top than pushing up from below which would equate to a net force. This force would start to accelerate the piece of metal downwards; there would be no equilibrium. Now forget about the piece of metal. Without it there would be air molecules rushing down from the pressure gradient. They would actually rush down until they equalized the pressure gradient and stopped moving.

Why does air pressure from above not crush us? The answer I see consistently given is that an equal air pressure from below balances it out.

This isn't quite correct. The pressure is not simply equal from above and below with your body being a zone of different pressure. Rather, your entire body is at the same pressure as the surroundings. To understand the difference, think about a tank from which some of the air can be evacuated (a vacuum tank). When the tank is full of air at equal pressure to the surroundings the lid can be removed easily. If you seal the container, pump some of the air out, and then try to remove the lid you will find that it is very tightly stuck. This is because there is a strong force on the lid caused by the pressure gradient between inside and outside.

The fact that your body is at atmospheric pressure is actually very important to the way it functions. If you were to be thrown out of a spaceship where the pressure is near zero, all of the gases (oxygen being an important one) would evaporate out of the fluids in your body.

Air pressure is exerted on the surface of a body by air molecules hitting the surface and being reflected. Each of these reflections (gazillions of which happen per second) transfers a little impulse on the surface, which macroscopically means a permanent force (per unit of area). Why do the air molecules bounce and hit all the time? Either because the air is moving at large (aka. "wind"), or because they bounce around irregularly (aka. "temperature"). The latter kind of movement knows no preferred direction and therefore the pressure is the same no matter what orientation the test surface has. The very fact that there is no net movement (wind) is expressed by the fact that the same force acts on the back side of a thin surface as on the front side (so there is no net force).

Then how come the air pressure is related to the weight of air above us? In equilibrum the force caused by air pressure from below on an imaginary horizontal surface is just enough to keep the air column above it "in place", whoich means that it equals the weight. We need not always have equilibrum, but if we don't then the stringer of the forces causes accelaration and movement - until equilibrum is reached.

I've tried to split up the questions a bit, drop a comment if I've missed something.

Air pressure is caused by the weight of the air molecules above.

This is indeed correct. The air pressure is proportional to how much air is above it: You have less on a high mountain than at sea level. The diagram shows this in practise.

Air pressure is equal in all directions.

This is also true: It will push equally in all directions. If it would be unequal, it would try to reach equilibrium. The air molecules will be subject to both the force of gravity pulling it towards earth (compressing it) and the force of other molecules, pushing it away.

For some little point in the atmosphere, this would be true. There would be equal force acting on it in all directions.

There is a very small difference for, say, a small cubed container since the bottom will have a tiny bit higher pressure from the air above it than the top side and the pressure will be marginally higher. However that decrease in pressure with altitude will take place both inside and outside the box. In general, the pressure difference can be ignored for almost all applications.

Pressure is given by the formula,

${P = {\rho}gh}$

${\rho}$ = density

${g}$ = gravitational constant

${h}$ = height/depth

Pressure at any point below the upper boundary of fluids, such as air and water, is uniform in all directions due to the fluid molecules being in constant motion and continually bumping into one another. Pressure increases with the depth of the fluid due to the amount of fluid above it, but any point on a horizontal plane will have the same pressure.

Compare this to rock in the Earth's crust and mantle. Ignoring tectonic stresses, the pressure in the vertical direction is still given by

However, because of the solid nature of rock, molecules are not rapidly moving and they do not continually bump into one another. Consequently, pressure in the lateral direction is not equal to the pressure in the vertical direction and pressure/stress in rock is not uniform in all directions.

This source gives the lateral pressure/stress as being related to the vertical pressure/stress.

${{\sigma}_h = k{\sigma}_v = k{\rho}gh}$

Air pressure is not caused by the weight of the air. It's caused by heat. Statistical physics has found that every particle has averagely energy kT/2 for every possible energy storing mechanism (NOTE1) which allow energy interchange between particles and mechanisms in a big mass of particles. k is Boltzman's constant and T is the temperature in kelvins. Climbing against gravity is one energy storing mechanism and that makes the air to float above the ground. Random translation motion in three dimensions give 3 mechanisms more. Molecule rotations and vibrations give even more.

kT/2 happens to be much more than what's needed to rip apart air particles from each other, so we have in normal temperatures gaseous air.

You meet the translation motion of the air particles and that pushes you equally from all directions if there's no systematic velocity component which we call wind. Wind is a phenomena which is caused by local temperature differences. In thermal equilibrium there's no wind.

You do not get crushed because you get so many small hits from every possible direction. Your body cannot retreat to any direction where the bombardment is non-existent. Your body, of course, squeezes a little due the bombardment, but that generates compensating opposite pressure with very little squeezing, so nothing visible happens. Now and then you relax your breathing muscles and allow some air to rush to your lungs to meet some oxygen extraction and carbon dioxide insertion. You will quite soon also press with the muscles the air out to make room for the next portion until one day...

Statistical physics allow also the possibility that all air particles near you happen to have the same translation direction - no direction is more probable than others, so it's possible that just one time every air particle around you happen to move to the same direction. In that case you may get crushed by a 3 bar one-directional pressure or thrown away if the state is valid in large enough area over a long enough time period. I guess the start and stop would have the most effect on you wellfare.

People who can handle statistical physics in math could calculate the probability of that state in the air in a given time period and volume. I guess the probability is quite low, because most getting crushed -cases have another explanation.

NOTE1: In physics textbooks they talk about "degrees of freedom"

• $\begingroup$ Thanks for providing this additional explanation from the statistical mechanics point of view that greatly complements those based on classical newtonian mechanics providinfg a more complete understanding of the phenomenon. $\endgroup$ –  MarcoD Commented Feb 18 at 10:56

Pressure is the average outward force that molecules exert on their surrounding.

If you take the case of air molecules bouncing around hitting everything they push outwards to the sides equally, but as you mentioned their weight means that they do indeed push downward harder than they push upwards. As the weight of air in a small space is very small, this difference can usually be neglected. However, without this difference balloons wouldn't float. This tiny difference adds up in the atmosphere till the pressures down here on the surface are actually pretty significant.

The reason the cars would squish you is that when the car pushes down with a high pressure, it will move your surface inward until you push back with the same pressure. Unfortunately for you, as your internal pressure increases that makes your sides at higher pressure than the air around you, so your sides squish out since the air doesn't push back as hard. So, it's not enough to just be pushed from the top and bottom, or even from four sides. You have to be pushed from all directions, including up your nose and inside your lungs in order for your internal pressure to be able to comfortably push back against the high pressure.

Both statements are correct. The best way to understand how these two statements can coexist is to understand the concept of a gas pressure.

Now to understand pressure we look at a container full of gas molecules. Gas molecules do not behave at all like solids or liquids. In a gas the molecules are not attracted to one another so they fly around at extreme speeds bouncing into objects and other gas molecules. These collisions are elastic so no energy is lost during collisions.

Every time a collision occurs some kind of energy transfer takes place between molecules. However, on a macroscopic level, there are so many collision taking place that they average out to zero energy transferred. Imagine that a gas molecule is about to hit the wall off the above container. We know that when the molecule hits it will bounce off and head in the other direction just like a bouncy ball. The wall will also feel a force due to Newton's second law . However on the other side of the container the exact same thing is happening. In fact the same thing is happening on the outside of the container as well. All these collisions exert a force but they all cancel each other out.

Now let us apply this to your first deffinition. As you stated air pressure is caused by the weight of the air molecules above. Gas molecules are attracted by gravity towards the earths surface. As a gas molecule is pulled toward the surface of the earth chances are it will hit another gas molecule and bounce off of it in another direction. Now lets say that in this particular collision the first molecule hits the top of the second molecule. This causes the second molecule to travel downwards even faster than the first molecule. This happens again and again until the molecule bounces of the surface of the earth. This is how your first definition is derived. The key is to remember that this is a gas pressure and thus is from all sides.

This is the hardest concept to grasp because when someone hears that there are hundreds of pounds of air above them they imagine hundreds of pounds of steel plates on their shoulders. Do not think of it like that. If a bouncy ball falls on your head it pushes you down. However if it misses, hits the floor, bounces up and hits you the two forces cancel each other out. The trick is to realize that so many collisions are occurring at such a minute scale that you do not "feel" the pressure of the atmosphere.

Solid objects are very good at resisting an even force from all directions. Have you ever heard that you can't crush an egg if you squeeze it from all directions? The same concept applies to to your body. The atmosphere is pushing very hard from all directions (even from inside your lungs!) but they all cancel out.

To contrast this imagine a steel drum with just a few gas molecules in it what would happen?

Now despite this being cool notice that the sides of the barrel collapse as well. This means that air molecules were pushing from the side but there was nothing to push back from the inside. We can see from the imploding barrel that the atmosphere is compressing us with enough force to crumple a steel drum. However because this pressure is exerted from every direction the forces are cancel out and we don't feel a thing.

I'd like to add my understanding, in case it helps anyone comprehend the reason. The reason there is pressure from all sides in these situations is due to the properties of fluids in equilibrium. In the atmosphere, for example, the air molecules being "weighted down on" from above would squeeze out the sides of the air column, if that were possible. It is not, of course, because the air column adjacent is under the same force and thus they are no better off. Gas molecules are energetic in every direction , or in other words, fluid pressure cannot exist in one direction if in equilibrium, as any difference in pressure would yield motion (wind).

The reason that you use the weight of the fluid above you (air, ocean, etc.) to know the horizontal pressure you would feel is because you are assuming you are in an area under equilibrium and thus you know from the above reasons that the "horizontal" pressure is equal to the "vertical" pressure.

Another intuition I like is the idea of a pneumatic piston. The cylinder that contains the fluid needs to be strong to keep from bursting. If you replaced the fluid with a metal rod and put piston force on that instead, the cylinder walls wouldn't feel anything.

Your Answer

Sign up or log in, post as a guest.

Required, but never shown

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy .

Not the answer you're looking for? Browse other questions tagged mechanical-engineering pressure or ask your own question .

• The Overflow Blog
• Scaling systems to manage all the metadata ABOUT the data
• Navigating cities of code with Norris Numbers
• Featured on Meta
• We've made changes to our Terms of Service & Privacy Policy - July 2024
• Bringing clarity to status tag usage on meta sites

Hot Network Questions

• Can I continue using technology after it is patented
• What was I thinking when I drew this diagram?
• Molecule that is placed on the equal sign
• Did Newton predict the deflection of light by gravity?
• How do I loosen this nut of my toilet lid?
• Why did Borland ignore the Macintosh market?
• Getting straight single quotes in a bibliography
• What counts as a pet?
• How can I obscure branding on the side of a pure white ceramic sink?
• When would it be legal to ask back (parts of) the salary?
• How can the Word be God and be with God simultaneously without creating the meaning of two Gods?
• Are the US or its European allies offering Iran anything in return for de-escalation?
• What is this fruit from Cambodia? (orange skin, 3cm, orange juicy flesh, very stick white substance)
• Communicate the intention to resign
• Why does Air Force Two lack a tail number?
• Counter in Loop
• How are USB-C cables so thin?
• Would several years of appointment as a lecturer hurt you when you decide to go for a tenure-track position later on?
• Will The Cluster World hold onto an atmosphere for a useful length of time without further intervention?
• Suitable tool bag for vintage centre pull brake bike
• Story about fishing for a sea monster on Venus
• Why does editing '/etc/shells' file using 'sudo open' show an error saying I don't own the file?
• What rule prevents a card from being played if its effect is known to be unresolvable?
• Why do individuals with revoked master’s/PhD degrees due to plagiarism or misconduct not return to retake them?

https://studynlearn.com/

Air exerts pressure- explanation with examples - science class 7.

As air is all around us, therefore all things experience air pressure. You would have experienced that cycling against the wind is really difficult. This is because of air pressure. You have learned that winds are actually caused by variations in air pressure. Let us learn how air exerts pressure?

Changes in air pressure bring changes in the weather and also result in the blowing of winds. Air usually moves from an area of high pressure to an area of low pressure and this produces winds. Very few of us realize how strong the air pressure can be. It can be really strong.

Air exerts pressure

Have you ever thought about why it is difficult to ride a bicycle against the direction of the wind? It happens because of air pressure. Let us do an activity to understand what is air pressure? Take a balloon and blow the air from your mouth into it. What made the balloon expand? Yes, this is because of the air you blow into it.

Air pressure inside the balloon is more than the pressure exerted by the air from outside. As a result, the balloon gets inflated. Air pressure is the pressure exerted by the air on different bodies. Actually, air exerts pressure on all bodies at all times in all directions.

Let us now recall some of the experiments.

When you fly a kite, does the wind coming from behind help?

Why is it easier to sail a boat if the wind is coming from behind it? You have to paddle so hard in the strong wind moving at high speed in the opposite direction because it creates air resistance. Due to air pressure only, leaves of trees, banners, and flags flatten when the wind blows across them.

Air pressure can even distort the shape of a bottle. Take a soft plastic bottle, fill it with hot water. Empty the bottle and immediately cap it tightly. Place the bottle under running water. Why does the bottle gets distorted?

As water is poured over the bottle some steam inside it condenses to form water. The air pressure inside the bottle is less than the pressure exerted by the air from outside. As a result, the bottle is crushed.

Now, let�s see an example.

Take a glass and fill it 1/3rd with water. Cover its mouth with an index card. Now, holding the glass carefully, invert the glass. Now, remove your hand from the card. You see that the card is stuck to the glass amazingly.

Do you know why it is the air pressure that is holding it up? The air outside the glass exerts upward pressure on the card.

As the pressure exerted by air outside is larger than the pressure exerted by the water and the air inside the glass. Consequently, the index card holds and water does not fall out.

Read More- Air Expands on Heating: Explanation with Examples - Science Class 7

• June,04 2021

Leave your comment

Reply Comment

In which direction does air exerts pressure?

The correct option is a in all directions air exerts pressure in all directions. gases exert pressure on the surface with which they come in contact. the pressure that a gas exerts on a surface is the result of gas particles colliding with the surface. since the gas particles move randomly in all directions, they exert pressure equally in all the directions..

How Does Air exerts pressure?

Some mustard oil is kept in a beaker. It will exert pressure: (a)downwards only (b) sideways only (c) upwards only (d) in all directions