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Remember Me Shop Experiment Kinetic Friction ExperimentsKinetic friction. Experiment #5 from Vernier Video Analysis: Motion and Sports IntroductionThe coefficient of friction is a measurement of the ease with which two materials slide past each other. Different combinations of materials have different coefficients of friction. For instance, the coefficient of friction between a bicycle’s rubber tire and a paved road surface is much greater than the coefficient of friction between a sled and snow. The coefficient of friction is usually given the Greek letter mu ( μ ) in mathematical relationships. Scientists have long recognized that the coefficient of friction is different when two objects are moving relative to each other or at rest. Imagine trying to slide a large refrigerator across a kitchen floor. It takes more force to get it moving than to keep it moving—this is because the coefficient of static (not moving) friction is greater than the coefficient of kinetic (sliding) friction. In this experiment, you will record video of a sliding object and use video analysis tools to determine the coefficient of kinetic friction. In this experiment, you will - Measure the motion of a sliding object.
- Evaluate the forces acting on a sliding object.
- Determine the coefficient of kinetic friction between the sliding object and the surface on which it is sliding based on the acceleration of the sliding object.
Sensors and EquipmentThis experiment features the following sensors and equipment. Additional equipment may be required. Ready to Experiment?Ask an expert. Get answers to your questions about how to teach this experiment with our support team. Purchase the Lab BookThis experiment is #5 of Vernier Video Analysis: Motion and Sports . The experiment in the book includes student instructions as well as instructor information for set up, helpful hints, and sample graphs and data. - Faculty Resource Center
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- 00:03 Overview
- 00:48 Principles of Friction
- 03:23 Measuring Friction Forces and Contributing Factors
- 05:31 Data Analysis and Results
- 07:11 Applications
- 08:04 Summary
Source: Nicholas Timmons, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA The goal of this experiment is to examine the physical nature of the two types of friction ( i.e., static and kinetic). The procedure will include measuring the coefficients of friction for objects sliding horizontally as well as down an inclined plane. Friction is not completely understood, but it is experimentally determined to be proportional to the normal force exerted on an object. If a microscope zooms in on two surfaces that are in contact, it would reveal that their surfaces are very rough on a small scale. This prevents the surfaces from easily sliding past one another. Combining the effect of rough surfaces with the electric forces between the atoms in the materials may account for the frictional force. There are two types of friction. Static friction is present when an object is not moving and some force is required to get that object in motion. Kinetic friction is present when an object is already moving but slows down due to the friction between the sliding surfaces. In this lab, two metal pans will be used to represent materials with different coefficients of friction. Block A will have a sand paper bottom, which will result in a higher coefficient of friction, while block B will have a smooth metal bottom. 1. Measure the coefficients of friction. - Add a 1,000-g weight to each block and use a scale measure the masses of blocks A and B, including the added mass.
- Repeat step 1.2 with block B.
- Repeat step 1.4 with block B.
2. Effect of weight on the force of friction. - Place block A on top of block B and repeat step 1.4 five times, determining the average value. Calculate the factor by which the frictional force increased/decreased.
- Place block B on top of block A and repeat step 1.4 five times, determining the average value. Calculate the factor by which the frictional force increased/decreased.
3. Effect of surface area on force of friction. - Turn block B onto the side that contains only the rim of the pan. The weight will need to be placed on the top of the face-up side. Measure the force of friction and compare it to the value measured in step 1.2. Calculate the factor by which the frictional force increased/decreased.
4. Angle of repose. - Place block A on the adjustable incline plane, starting at an angle of 0°. Slowly raise the angle until the block begins to slide. Using a protractor, measure the angle of repose and use Equation 3 to calculate the coefficient of static friction just before the block began to slide. Do this five times and record the average value.
- Repeat step 4.2 with block B.
The effects of friction are easily observed in everyday activities and yet the physical mechanisms that govern friction can be complex. Friction is a force that opposes the motion of an object when it is in contact with a surface. At the microscopic level, it is caused by surface roughness of the materials in contact and intermolecular interactions. But one can overcome this force by application of an external force that is equal in magnitude. The goal of this video is to demonstrate how to measure friction in a lab setting for objects sliding horizontally as well as down an inclined plane. Before diving into the protocol, let’s revisit the concepts behind the frictional force. First, you need to know that there are two types of frictions – kinetic friction and static friction. To understand kinetic friction, imagine you are in a rubber tube sliding across an infinite horizontal field of ice. Although ice may be considered a smooth surface, if we look at the microscopic level, there are complex interactions between the two surfaces that cause friction. These interactions depend on surface roughness and attractive intermolecular forces. The magnitude of this kinetic friction force is equal to the product of the coefficient of kinetic friction, or μK, which depends on the material-surface combination, and the normal force, or Fnorm that pushes the object and surface together. Fnorm acts to support the object and is perpendicular to the interface. In this case, since the tube is on a level ground, the Fnorm is equal to and opposite the force of gravity, which is mg . Therefore, if you know the combined mass of you with the tube, and the coefficient of kinetic friction for rubber and ice, we can easily calculate the force of friction. Kinetic friction can convert some of the tube’s kinetic energy into heat and will also reduce the momentum of the tube ultimately bringing it to rest. Now, this is when static friction – the other type of friction – comes into play. This frictional force opposes movement of a static object and could be calculated by applying an external force. The applied force that eventually moves the object reveals the maximum static force . The formula for maximum static force is the same as the one for kinetic friction, but the coefficient of static friction μS is typically greater than μK for the same material-surface combination. Another way to overcome the maximum static force is by increasing the slope of the surface. At some angle, called the angle of repose or θR, the force pulling down the slope will equal the static friction force and the tube will begin to slide. This pulling force, which is the sine of the angle of repose times the force of gravity, equals the maximum static force, which is μS times product of m , g, and cosine of θR. By rearranging this equation, we can calculate the coefficient of static friction. Now that we’ve learned the principles of friction, let’s see how these concepts can be applied to experimentally calculate the forces and coefficients of both kinetic and static friction. This experiment consists of a mass scale, a force scale, two metal pans with different coefficients of friction denoted as block 1 and 2, an adjustable incline plane, two 1000 g weights, and a protractor. Add a 1000 g weight to each block and use the scale to measure the masses of the loaded blocks. After connecting the force scale to block 1, pull the scale horizontally and note the force reading just before the block begins to slide. Record this maximal static friction force and repeat this measurement five times to obtain multiple data sets. Perform the same procedure using block 2 and record these values. Next, with the force scale connected to block 1, pull the scale at a constant speed and note the kinetic friction force on the gauge. Repeat this measurement five times to obtain multiple data sets. Again, perform the same procedure using block 2 and record these values. Now, place block 1 on top of block 2 and pull the scale at a constant speed to determine the kinetic friction force. Repeat this measurement five times and calculate the average. Then perform the same procedure with block 2 on top of block 1. For the next experiment, turn block 1 such that the smaller surface area faces the table and attach it to the force scale. Now measure the static friction force as before by making note of the force before the block begins to slide. Repeat this measurement five times to obtain multiple data sets. For the last experiment, place block 1 on the adjustable incline plane with the plane initially at an angle of zero degrees. Slowly raise the angle of the plane and use a protractor to determine the angle at which the block begins to slide. Again, repeat this measurement five times to obtain multiple data sets and perform the same procedure using block 2. For the experiments performed on horizontal surface, the normal force on the blocks is equal to the weight, that is mass times g . Since the mass of block 1 and 2 for both static and kinetic friction experiments are the same, Fnorm is the same in all four cases. Using the average of the measured force values for the various experiments, and the formulae for both frictions, the coefficients of friction can be calculated. As expected, the coefficient of static friction is greater than the coefficient of kinetic friction. Furthermore, the respective coefficients for the two blocks are different since they each possess a different surface roughness. In the stacked blocks experiment, we know that the mass doubles in both cases, so we can calculate the new Fnorm. We already know μk for the block in contact with the surface. Using this we can calculate the kinetic friction force, which agrees well with the measured force during the experiment. The friction force measured following a change in orientation of block 1 demonstrated that the contact surface area does not affect the force of friction. The discrepancies between the calculated and measured forces are consistent with the estimated errors associated with reading the force scale while maintaining a constant speed. For the inclined plane experiments, the angle of repose was measured. Using this angle, the coefficients of static friction could be determined, and here the values compare favorably with the coefficients measured from the horizontal sliding measurements. Studying friction is important in several applications, as it can either be highly beneficial or a phenomenon that must be minimized. It is extremely important for automobile tire manufactures to study friction, as it allows tires to gain traction on a road. Therefore, when it rains, the water and residual oils on the road significantly reduce the coefficient of friction, making sliding and accidents much more likely. While engineers want to increase friction for car tires, for engines and machinery in general they want to reduce it, as friction between metals can generate heat and damage their structures. Therefore, engineers constantly study lubricants that may help in decreasing the coefficient of friction between two surfaces. You’ve just watched JoVE’s introduction to Friction. You should now understand what factors contribute to the magnitude of friction, the different types of friction, and the underlying physical mechanisms that govern it. As always, thanks for watching! Table 1. Coefficients of friction. Block | | | A | 0.68 | 0.60 | B | 0.52 | 0.47 | Table 2. Effect of weight and surface area on the force of friction. Measurement | | Factor by which it is larger or smaller | Block B on A | 16 | With | Block A on B | 14 | With | Small surface area | 5 | With | Table 3. Angle of repose. Block | Angle of repose | | A | 30 | 0.58 | B | 24 | 0.45 | The results obtained from the experiment match the predictions made by Equations 1 and 2 . In step 1, the static friction was larger than the kinetic friction. This is always the case, as more force is required to overcome friction when an object is not already in motion. In step 2, it was confirmed that the force of friction was proportional to the weight of both blocks and the coefficient of kinetic friction of the block in contact with the table. The result of step 3 confirms that the surface area does not affect the force of friction. In step 4, the angle of repose can be approximated by Equation 3 . The error associated with the lab comes from the difficulty of reading the force scale while maintaining a constant velocity for the sliding block. By taking several measurements and calculating the average, this effect can be reduced. Applications and SummaryFriction is everywhere in our daily lives. In fact, it would not be possible to walk without it. If someone tried walking on a frictionless surface, he would go nowhere. It is only the friction between the bottom of his feet and the ground as his muscles push against the ground that propels him forward. In almost every aspect of industry, engineers are trying to reduce friction. When two surfaces are in contact, there will always be friction. This can take the form of heat, such as the heat felt when someone quickly rubs her hands together. In industrial applications, this heat can damage machines. Friction forces also oppose the motion of objects and can slow done mechanical operations. Therefore, substances like lubricants are used to decrease the coefficient of friction between two surfaces. Table 4. Example coefficients of friction. Materials | | wood on wood | 0.2 | brass on steel | 0.44 | rubber on concrete | 0.8 | lubricated ball bearings | < 0.01 | In this experiment, the coefficients of static and kinetic friction were measured for two different sliding blocks. The effect of mass on the force of friction was examined, along with the effect of surface area. Lastly, the angle of repose for a block on an inclined plane was measured. The magnitude of this kinetic friction force is equal to the product of the coefficient of kinetic friction, or μK, which depends on the material-surface combination, and the normal force, or Fnorm that pushes the object and surface together. Fnorm acts to support the object and is perpendicular to the interface. In this case, since the tube is on a level ground, the Fnorm is equal to and opposite the force of gravity, which is mg. Therefore, if you know the combined mass of you with the tube, and the coefficient of kinetic friction for rubber and ice, we can easily calculate the force of friction. Now, this is when static friction – the other type of friction – comes into play. This frictional force opposes movement of a static object and could be calculated by applying an external force. The applied force that eventually moves the object reveals the maximum static force. The formula for maximum static force is the same as the one for kinetic friction, but the coefficient of static friction μS is typically greater than μK for the same material-surface combination. Another way to overcome the maximum static force is by increasing the slope of the surface. At some angle, called the angle of repose or θR, the force pulling down the slope will equal the static friction force and the tube will begin to slide. This pulling force, which is the sine of the angle of repose times the force of gravity, equals the maximum static force, which is μS times product of m, g, and cosine of θR. By rearranging this equation, we can calculate the coefficient of static friction. For the experiments performed on horizontal surface, the normal force on the blocks is equal to the weight, that is mass times g. Since the mass of block 1 and 2 for both static and kinetic friction experiments are the same, Fnorm is the same in all four cases. Using the average of the measured force values for the various experiments, and the formulae for both frictions, the coefficients of friction can be calculated. In the stacked blocks experiment, we know that the mass doubles in both cases, so we can calculate the new Fnorm. We already know μk for the block in contact with the surface. Using this we can calculate the kinetic friction force, which agrees well with the measured force during the experiment. | | | | Existing users log in or new users sign up . | | | | | | | | | | | | | | | | | | | |
Finding the coefficient of friction: Application ExperimentDetermine the coefficient of kinetic friction between the tissue box and the table. Prior Knowledge- Conservation of momentum
- Transformation of energy
- Kinetic energy, gravitational potential energy, internal energy, work
- Friction force, static friction force, kinetic friction force
Description of the ExperimentObserve the two experiments below. Use each to determine the coefficient of kinetic friction between the tissue box and the table. List all of the assumptions that you made. Describe how you will use the video to determine the necessary quantities. List all physics explanations/relationships you will use to determine the coefficient of friction. Describe the mathematical procedure that you will use to find the coefficient of kinetic friction from the measured physical quantities. Decide whether you have a reasonable agreement between the results of the two experiments. Addtional InformationCarefully examine the assumptions that you use. The flour-filled balloon has a mass of 54.7g, the tissue-box has a mass of 161.1g. | Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click . | - What physics explanations/relationships did you use to find the coefficient of friction?
- Did the assumptions that you made allow you to use these explanations/relationships?
- Describe the processes that occurred in the second experiment from the point of view of energy. What is the system that you chose for your analysis?
- Describe the processes that occurred in the second experiment from the point of view of momentum. What is the system that you chose for your analysis?
- Did the results from the two experiments match? If not, how do you need to modify your assumptions to change the mathematical procedure?
© 2015 Rutgers, The State University of New Jersey. All rights reserved. | 6.2 FrictionLearning objectives. By the end of this section, you will be able to: - Describe the general characteristics of friction
- List the various types of friction
- Calculate the magnitude of static and kinetic friction, and use these in problems involving Newton’s laws of motion
When a body is in motion, it has resistance because the body interacts with its surroundings. This resistance is a force of friction. Friction opposes relative motion between systems in contact but also allows us to move, a concept that becomes obvious if you try to walk on ice. Friction is a common yet complex force, and its behavior still not completely understood. Still, it is possible to understand the circumstances in which it behaves. Static and Kinetic FrictionThe basic definition of friction is relatively simple to state. Friction is a force that opposes relative motion between systems in contact. There are several forms of friction. One of the simpler characteristics of sliding friction is that it is parallel to the contact surfaces between systems and is always in a direction that opposes motion or attempted motion of the systems relative to each other. If two systems are in contact and moving relative to one another, then the friction between them is called kinetic friction. For example, friction slows a hockey puck sliding on ice. When objects are stationary, static friction can act between them; the static friction is usually greater than the kinetic friction between two objects. If two systems are in contact and stationary relative to one another, then the friction between them is called static friction . If two systems are in contact and moving relative to one another, then the friction between them is called kinetic friction . Imagine, for example, trying to slide a heavy crate across a concrete floor—you might push very hard on the crate and not move it at all. This means that the static friction responds to what you do—it increases to be equal to and in the opposite direction of your push. If you finally push hard enough, the crate seems to slip suddenly and starts to move. Now static friction gives way to kinetic friction. Once in motion, it is easier to keep it in motion than it was to get it started, indicating that the kinetic frictional force is less than the static frictional force. If you add mass to the crate, say by placing a box on top of it, you need to push even harder to get it started and also to keep it moving. Furthermore, if you oiled the concrete you would find it easier to get the crate started and keep it going (as you might expect). Figure 6.10 is a crude pictorial representation of how friction occurs at the interface between two objects. Close-up inspection of these surfaces shows them to be rough. Thus, when you push to get an object moving (in this case, a crate), you must raise the object until it can skip along with just the tips of the surface hitting, breaking off the points, or both. A considerable force can be resisted by friction with no apparent motion. The harder the surfaces are pushed together (such as if another box is placed on the crate), the more force is needed to move them. Part of the friction is due to adhesive forces between the surface molecules of the two objects, which explains the dependence of friction on the nature of the substances. For example, rubber-soled shoes slip less than those with leather soles. Adhesion varies with substances in contact and is a complicated aspect of surface physics. Once an object is moving, there are fewer points of contact (fewer molecules adhering), so less force is required to keep the object moving. At small but nonzero speeds, friction is nearly independent of speed. The magnitude of the frictional force has two forms: one for static situations (static friction), the other for situations involving motion (kinetic friction). What follows is an approximate empirical (experimentally determined) model only. These equations for static and kinetic friction are not vector equations. Magnitude of Static FrictionThe magnitude of static friction f s f s is where μ s μ s is the coefficient of static friction and N is the magnitude of the normal force. The symbol ≤ ≤ means less than or equal to , implying that static friction can have a maximum value of μ s N . μ s N . Static friction is a responsive force that increases to be equal and opposite to whatever force is exerted, up to its maximum limit. Once the applied force exceeds f s (max), f s (max), the object moves. Thus, Magnitude of Kinetic FrictionThe magnitude of kinetic friction f k f k is given by where μ k μ k is the coefficient of kinetic friction . A system in which f k = μ k N f k = μ k N is described as a system in which friction behaves simply . The transition from static friction to kinetic friction is illustrated in Figure 6.11 . As you can see in Table 6.1 , the coefficients of kinetic friction are less than their static counterparts. The approximate values of μ μ are stated to only one or two digits to indicate the approximate description of friction given by the preceding two equations. System | Static Friction | Kinetic Friction | Rubber on dry concrete | 1.0 | 0.7 | Rubber on wet concrete | 0.5-0.7 | 0.3-0.5 | Wood on wood | 0.5 | 0.3 | Waxed wood on wet snow | 0.14 | 0.1 | Metal on wood | 0.5 | 0.3 | Steel on steel (dry) | 0.6 | 0.3 | Steel on steel (oiled) | 0.05 | 0.03 | Teflon on steel | 0.04 | 0.04 | Bone lubricated by synovial fluid | 0.016 | 0.015 | Shoes on wood | 0.9 | 0.7 | Shoes on ice | 0.1 | 0.05 | Ice on ice | 0.1 | 0.03 | Steel on ice | 0.04 | 0.02 | Equation 6.1 and Equation 6.2 include the dependence of friction on materials and the normal force. The direction of friction is always opposite that of motion, parallel to the surface between objects, and perpendicular to the normal force. For example, if the crate you try to push (with a force parallel to the floor) has a mass of 100 kg, then the normal force is equal to its weight, perpendicular to the floor. If the coefficient of static friction is 0.45, you would have to exert a force parallel to the floor greater than to move the crate. Once there is motion, friction is less and the coefficient of kinetic friction might be 0.30, so that a force of only keeps it moving at a constant speed. If the floor is lubricated, both coefficients are considerably less than they would be without lubrication. Coefficient of friction is a unitless quantity with a magnitude usually between 0 and 1.0. The actual value depends on the two surfaces that are in contact. Many people have experienced the slipperiness of walking on ice. However, many parts of the body, especially the joints, have much smaller coefficients of friction—often three or four times less than ice. A joint is formed by the ends of two bones, which are connected by thick tissues. The knee joint is formed by the lower leg bone (the tibia) and the thighbone (the femur). The hip is a ball (at the end of the femur) and socket (part of the pelvis) joint. The ends of the bones in the joint are covered by cartilage, which provides a smooth, almost-glassy surface. The joints also produce a fluid (synovial fluid) that reduces friction and wear. A damaged or arthritic joint can be replaced by an artificial joint ( Figure 6.12 ). These replacements can be made of metals (stainless steel or titanium) or plastic (polyethylene), also with very small coefficients of friction. Natural lubricants include saliva produced in our mouths to aid in the swallowing process, and the slippery mucus found between organs in the body, allowing them to move freely past each other during heartbeats, during breathing, and when a person moves. Hospitals and doctor’s clinics commonly use artificial lubricants, such as gels, to reduce friction. The equations given for static and kinetic friction are empirical laws that describe the behavior of the forces of friction. While these formulas are very useful for practical purposes, they do not have the status of mathematical statements that represent general principles (e.g., Newton’s second law). In fact, there are cases for which these equations are not even good approximations. For instance, neither formula is accurate for lubricated surfaces or for two surfaces sliding across each other at high speeds. Unless specified, we will not be concerned with these exceptions. Example 6.10Here we are using the symbol f to represent the frictional force since we have not yet determined whether the crate is subject to station friction or kinetic friction. We do this whenever we are unsure what type of friction is acting. Now the weight of the crate is which is also equal to N . The maximum force of static friction is therefore ( 0.700 ) ( 196 N ) = 137 N . ( 0.700 ) ( 196 N ) = 137 N . As long as P → P → is less than 137 N, the force of static friction keeps the crate stationary and f s = P → . f s = P → . Thus, (a) f s = 20.0 N, f s = 20.0 N, (b) f s = 30.0 N, f s = 30.0 N, and (c) f s = 120.0 N . f s = 120.0 N . (d) If P → = 180.0 N, P → = 180.0 N, the applied force is greater than the maximum force of static friction (137 N), so the crate can no longer remain at rest. Once the crate is in motion, kinetic friction acts. Then and the acceleration is SignificanceCheck your understanding 6.7. A block of mass 1.0 kg rests on a horizontal surface. The frictional coefficients for the block and surface are μ s = 0.50 μ s = 0.50 and μ k = 0.40 . μ k = 0.40 . (a) What is the minimum horizontal force required to move the block? (b) What is the block’s acceleration when this force is applied? Friction and the Inclined PlaneOne situation where friction plays an obvious role is that of an object on a slope. It might be a crate being pushed up a ramp to a loading dock or a skateboarder coasting down a mountain, but the basic physics is the same. We usually generalize the sloping surface and call it an inclined plane but then pretend that the surface is flat. Let’s look at an example of analyzing motion on an inclined plane with friction. Example 6.11Downhill skier. Substituting this into our expression for kinetic friction, we obtain which can now be solved for the coefficient of kinetic friction μ k . μ k . Substituting known values on the right-hand side of the equation, We have discussed that when an object rests on a horizontal surface, the normal force supporting it is equal in magnitude to its weight. Furthermore, simple friction is always proportional to the normal force. When an object is not on a horizontal surface, as with the inclined plane, we must find the force acting on the object that is directed perpendicular to the surface; it is a component of the weight. We now derive a useful relationship for calculating coefficient of friction on an inclined plane. Notice that the result applies only for situations in which the object slides at constant speed down the ramp. An object slides down an inclined plane at a constant velocity if the net force on the object is zero. We can use this fact to measure the coefficient of kinetic friction between two objects. As shown in Example 6.11 , the kinetic friction on a slope is f k = μ k m g cos θ f k = μ k m g cos θ . The component of the weight down the slope is equal to m g sin θ m g sin θ (see the free-body diagram in Figure 6.14 ). These forces act in opposite directions, so when they have equal magnitude, the acceleration is zero. Writing these out, Solving for μ k , μ k , we find that Put a coin on a book and tilt it until the coin slides at a constant velocity down the book. You might need to tap the book lightly to get the coin to move. Measure the angle of tilt relative to the horizontal and find μ k . μ k . Note that the coin does not start to slide at all until an angle greater than θ θ is attained, since the coefficient of static friction is larger than the coefficient of kinetic friction. Think about how this may affect the value for μ k μ k and its uncertainty. Atomic-Scale Explanations of FrictionThe simpler aspects of friction dealt with so far are its macroscopic (large-scale) characteristics. Great strides have been made in the atomic-scale explanation of friction during the past several decades. Researchers are finding that the atomic nature of friction seems to have several fundamental characteristics. These characteristics not only explain some of the simpler aspects of friction—they also hold the potential for the development of nearly friction-free environments that could save hundreds of billions of dollars in energy which is currently being converted (unnecessarily) into heat. Figure 6.15 illustrates one macroscopic characteristic of friction that is explained by microscopic (small-scale) research. We have noted that friction is proportional to the normal force, but not to the amount of area in contact, a somewhat counterintuitive notion. When two rough surfaces are in contact, the actual contact area is a tiny fraction of the total area because only high spots touch. When a greater normal force is exerted, the actual contact area increases, and we find that the friction is proportional to this area. However, the atomic-scale view promises to explain far more than the simpler features of friction. The mechanism for how heat is generated is now being determined. In other words, why do surfaces get warmer when rubbed? Essentially, atoms are linked with one another to form lattices. When surfaces rub, the surface atoms adhere and cause atomic lattices to vibrate—essentially creating sound waves that penetrate the material. The sound waves diminish with distance, and their energy is converted into heat. Chemical reactions that are related to frictional wear can also occur between atoms and molecules on the surfaces. Figure 6.16 shows how the tip of a probe drawn across another material is deformed by atomic-scale friction. The force needed to drag the tip can be measured and is found to be related to shear stress , which is discussed in Static Equilibrium and Elasticity . The variation in shear stress is remarkable (more than a factor of 10 12 10 12 ) and difficult to predict theoretically, but shear stress is yielding a fundamental understanding of a large-scale phenomenon known since ancient times—friction. InteractiveEngaging the simulation below, describe a model for friction on a molecular level. Describe matter in terms of molecular motion. The description should include diagrams to support the description; how the temperature affects the image; what are the differences and similarities between solid, liquid, and gas particle motion; and how the size and speed of gas molecules relate to everyday objects. Example 6.12Sliding blocks. Solving for the two unknowns, we obtain N 1 = 19.6 N N 1 = 19.6 N and T = 0.40 N 1 = 7.84 N . T = 0.40 N 1 = 7.84 N . The bottom block is also not accelerating, so the application of Newton’s second law to this block gives The values of N 1 N 1 and T were found with the first set of equations. When these values are substituted into the second set of equations, we can determine N 2 N 2 and P . They are Example 6.13A crate on an accelerating truck. - Application of Newton’s second law to the crate, using the reference frame attached to the ground, yields ∑ F x = m a x ∑ F y = m a y f s = ( 50.0 kg ) ( 2.00 m/s 2 ) N − 4.90 × 10 2 N = ( 50.0 kg ) ( 0 ) = 1.00 × 10 2 N N = 4.90 × 10 2 N . ∑ F x = m a x ∑ F y = m a y f s = ( 50.0 kg ) ( 2.00 m/s 2 ) N − 4.90 × 10 2 N = ( 50.0 kg ) ( 0 ) = 1.00 × 10 2 N N = 4.90 × 10 2 N . We can now check the validity of our no-slip assumption. The maximum value of the force of static friction is μ s N = ( 0.400 ) ( 4.90 × 10 2 N ) = 196 N, μ s N = ( 0.400 ) ( 4.90 × 10 2 N ) = 196 N, whereas the actual force of static friction that acts when the truck accelerates forward at 2.00 m/s 2 2.00 m/s 2 is only 1.00 × 10 2 N . 1.00 × 10 2 N . Thus, the assumption of no slipping is valid.
- If the crate is to move with the truck when it accelerates at 5.0 m/s 2 , 5.0 m/s 2 , the force of static friction must be f s = m a x = ( 50.0 kg ) ( 5.00 m/s 2 ) = 250 N . f s = m a x = ( 50.0 kg ) ( 5.00 m/s 2 ) = 250 N . Since this exceeds the maximum of 196 N, the crate must slip. The frictional force is therefore kinetic and is f k = μ k N = ( 0.300 ) ( 4.90 × 10 2 N ) = 147 N . f k = μ k N = ( 0.300 ) ( 4.90 × 10 2 N ) = 147 N . The horizontal acceleration of the crate relative to the ground is now found from ∑ F x = m a x 147 N = ( 50.0 kg ) a x , so a x = 2.94 m/s 2 . ∑ F x = m a x 147 N = ( 50.0 kg ) a x , so a x = 2.94 m/s 2 .
Example 6.14Snowboarding. From the second equation, N = m g cos θ . N = m g cos θ . Upon substituting this into the first equation, we find Check Your Understanding 6.8The snowboarder is now moving down a hill with incline 10.0 ° 10.0 ° . What is the snowboarder's acceleration? This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission. Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax. Access for free at https://openstax.org/books/university-physics-volume-1/pages/1-introduction - Authors: William Moebs, Samuel J. Ling, Jeff Sanny
- Publisher/website: OpenStax
- Book title: University Physics Volume 1
- Publication date: Sep 19, 2016
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- Book URL: https://openstax.org/books/university-physics-volume-1/pages/1-introduction
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© Jul 23, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University. Teacher Resource CenterPasco partnerships. 2024 Catalogs & BrochuresCoefficients of friction. Experimentally determine the static and kinetic friction coefficients between two contacting surfaces. Grade Level: Advanced Placement • High School Subject: Physics Student Files Teacher Files Sign In to your PASCO account to access teacher files and sample data. Standards Correlations Topics | Topics | 2.2 | 3.C.4.1; 3.C.4.2 | Featured EquipmentFriction BlockReplacement friction block for the Introductory Dynamics Systems (ME-9429A, ME-9452). Smart Cart (Blue)The Smart Cart is the ultimate tool for your physics lab with built-in sensors that measure force, position, velocity, three axes of acceleration, and three axes of rotational velocity. U.S. Patent No. 10,481,173 Smart Cart (Red)The Smart Cart is the ultimate tool for your physics lab and includes built-in sensors for measuring force, position, velocity, three axes of acceleration, and three axes of rotational velocity. Patent No. 10481173 Many lab activities can be conducted with our Wireless , PASPORT , or even ScienceWorkshop sensors and equipment. For assistance with substituting compatible instruments, contact PASCO Technical Support . We're here to help. Copyright © 2023 PASCO Source Collection: Lab #05 Physics Lab Station: Mechanics StarterMore experiments. - Transistors
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By graphing these data, coefficients of static and kinetic friction will be obtained. As you perform this experiment, theoretical quanti-ties will be determined prior to measuring for Part 2 through Part 5.
where fk, the kinetic friction force, is exerted tangent to the surface and opposite to its direction of motion. Here, N is the force that one surface exerts normal to the other surface, and k, the coefficient of kinetic friction, depends only on the intrinsic properties of the two surfaces in contact. [1] The purpose of this experiment is to determine the coefficient of kinetic friction be ...
The force of kinetic friction is otherwise known as sliding friction, and it describes the resistance to motion caused by the interaction between an object and the surface it's moving on. You can calculate the kinetic friction force based on the specific coefficient of friction and the normal force.
Both static and kinetic friction depend on the surfaces of the box and the floor, and on how hard the box and floor are pressed together. We model kinetic friction with Fkinetic = µk N, where µk is the coefficient of kinetic friction. In this experiment, you will use a Dual-Range Force Sensor to study static friction and kinetic friction on a ...
0:00 Learning Goals1:27 Data from Experiment3:08 Table/Equations for Acceleration3:35 Calculate Angle of Inclination 4:29 Force diagram7:35 Components of Gra...
This experiment will introduce the student to a simple method for measuring the coe cients of static and kinetic friction between two surfaces. The experiment is sensitive and care must be taken to obtain good results. The general principle behind the experiment is to determine the coe cients of static and kinetic friction between two surfaces by varying the mass of a block of material and ...
where fk, the kinetic friction force, is exerted tangent to the surface and opposite to its direction of motion. Here N is the force that one surface exerts normal to the other surface, and k, the coe cient of kinetic friction, depends only on the intrinsic properties of the two surfaces in contact.[1]
The coefficient of kinetic friction can be determined through experiments, such as measuring the force needed to overcome friction or measuring the angle at which an object will start to slide off an incline.
In this section of the experiment you will use your knowledge of obtaining the coefficient of kinetic friction on an incline plane to determine the coefficient of static friction between two layers of sand. First fill up a cup with dry sand and slowly pour it onto a piece of paper covering the top of your lab station.
It takes more force to get it moving than to keep it moving—this is because the coefficient of static (not moving) friction is greater than the coefficient of kinetic (sliding) friction. In this experiment, you will record video of a sliding object and use video analysis tools to determine the coefficient of kinetic friction.
Description of the Experiment Observe the two experiments below. Use each to determine the coefficient of kinetic friction between the tissue box and the table. List all of the assumptions that you made. Describe how you will use the video to determine the necessary quantities.
In this experiment, the frictional force between a wooden block and the wooden surface of a horizontal and inclined plane will be measured, and from these plotted data, the coefficients of static and kinetic friction will be obtained.
The coefficient of friction must be measured experimentally and is a property that depends upon the two materials that are in contact. There are two types of coefficients of friction: kinetic friction, , when objects are already in motion, and static friction, , when objects are at rest and require a certain amount of force to get moving.
Friction is a force that is around us all the time that opposes relative motion between surfaces in contact but also allows us to move (which you have d...
The purpose of this lab is to construct a relationship between frictional forces and the normal force on an object, to calculate the kinetic and static coe cients of friction for various objects and surfaces and to ultimately gain a solid understanding of static vs kinetic friction.
Describe the mathematical procedure that you will use to find the coefficient of kinetic friction from the measured physical quantities. Decide whether you have a reasonable agreement between the results of the two experiments.
The coefficient of friction (fr) is a number that is the ratio of the resistive force of friction (Fr) divided by the normal or perpendicular force (N) pushing the objects together. It is represented by the equation: fr= Fr/N.
There are several forms of friction. One of the simpler characteristics of sliding friction is that it is parallel to the contact surfaces between syste...
Friction Lab. This lab will let you determine the coefficients of static friction and kinetic friction between different surfaces. You will be pulling with increasing tension until the object begins to slide and then you will keep the object moving at a slow steady speed. The graph below the action is a graph of the tension in the string.
Introducing the Mini Lab for Friction: Measuring the Coefficient of Kinetic Friction David Schalek 573 subscribers Subscribed Like 10K views 3 years ago PALISADES CHARTER HIGH SCHOOL ...more
Purpose (1) To become familiar with the concepts of static and kinetic friction. (2) To measure the coefficients of static and kinetic friction for a plane.
Experimentally determine the static and kinetic friction coefficients between two contacting surfaces.
A lab report on a friction experiment. the calculation of the coefficient of friction in laboratory setting nienke adamse abstract the purpose of this
Work and Kinetic Energy Up until now, we have assumed that the force is constant and thus, the accelera-tion is constant. Is there a simple technique for dealing with non-constant forces? Fortunately, the answer is, \Yes." In this chapter, we will introduce the following concepts: 1.work 2.kinetic energy 3.the connection between work and ...