Calculate acceleration of the block.

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1 Physics, Mr. Kent Daily Worksheet: Friction Name: 1. A ball rolling on a horizontal surface slows down because of between the and the. 2. A sky diver slows down because of between the and the. That is, is a type of friction. 3. Friction is a. 4. Friction is a that motion. 5. So if an object moves East across a surface, the force of friction is exerted. If a force is directed to the right, the force of friction is exerted. 6. Draw the diagram on the board. Then: F net = Calculate acceleration of the block. 7. It s harder to over a surface than it is to that same object moving over the same surface. 8. There are two types of friction. Circle the one that is larger. Movement Friction 9. Symbols for friction: Static Friction: Kinetic Friction: 10. Draw 2 free body diagrams, label the forces. Use a thicker arrow for a larger force: A gnome pulls on a block across a surface. Drawing 1: His force just before the block moving. Drawing 2: Later he moves the block across the floor with less force.

2 11. friction is an force because it s. If an object on a surface is pushed or pulled with a force, static friction will push back with that force. Since the 2 forces they are and the object doesn t. Static friction will and continue to the push or pull until the push or pull reaches its. Only then will the object. 12. A 200 kg block rests on a cement floor. The maximum static friction between the block and the floor is 350 N. Complete the following table: Push or Pull Force Static Friction (f s ) Net Force (F net ) Movement 100 N 200 N 300 N 400 N At what rate will the block accelerate with a push pr pull force of 400 N? 13. Order these from lowest friction to highest friction: a. 90 kg block of wood on a cement floor b. 50 kg block of wood on a cement floor c. 50 kg block of wood on ice d. 50 kg block of ice on ice 14. What, then, are the two factors that affect friction? a. b. 15. Different of surfaces have different amounts of. The amount of friction from a pair of is indicated by the pair s of. 16. The greek letter ( ) is used to represent coefficients of. 17. Symbols: a. Coefficient of static friction: Coefficient of static friction:

3 18. Refer to this table of coefficients of friction regarding pairs of surfaces: Pair with the greatest static friction: Pair with the greatest kinetic friction: Pair with the smallest static friction: Pair with the smallest kinetic friction: Does the highest static friction always mean the highest kinetic friction? 19. Whenever a force is exerted on a the surface pushes back with a force called the force ( ). 20. The most common force on a is an object s. When an object is on a surface its weight pushes and the surface exerts a up equal to. If the surface is then: a. The forces are b. The object is in c. The object doesn t 21. Normal Force is to the surface that exerts it. So, if an object rests on a surface, then does not equal the object s. 22. In most of our problems, objects will reside on surfaces. So, = and we can use in our friction calculations. 23. A 90 kg block sits on a horizontal surface. Weight? Direction: Normal force (F N )? Direction:

4 24. Formula for Static Friction: For Kinetic Friction: 25. A 200 kg steel block sits on a copper surface. a. s = k = b. F N = c. f s = f k = 26. Chelsea exerts a force of 800 N to pull a 125 kg aluminum block across a steel surface. F N = f s = Will the block move? f k = F net while moving = Acceleration = 27. Franky exerts a force of 725 N to pull a 75 kg glass block across a glass surface. F N = f s = Will the block move? f k = F net while moving = Acceleration =

5 Physics, Mr. Kent Classwork: Friction Name: 1. Friction is a 2. Definition of friction: 3. There are two types of friction: a. occurs when an object is b. occurs when an object is 4. Which type of friction is larger? 5. So, if you push a desk across a floor, which requires more force? (a) Getting the desk moving (b) Keeping the desk moving. Explain: 6. Kayla decides to push 200 kg bookshelf across the tile floor of her basement. She has to push very hard (F = 300 N) to get the bookshelf moving. Once it is moving, however, pushing it it fairly easy (F = 175 N). She keeps pushing, however at 300 N. a. Maximum static friction: b. Kinetic Friction: c.. F Net while moving: d. Acceleration of the shelf: 7. Kayla thinks back to exactly what she did. At first, she pushed with a small force (100 N). When this didn t work she pushed progressively harder: With a force of 175 N then 250 N and finally 300 N. Complete the following table F Push f s F Net Movement 8. When an object sits on a surface the force of its is exerted on the surface. We know from Newton s 3rd Law that for every force there is an. What

6 is the name of the equal and opposite force to the weight of an object sitting on a surface?. Abbreviation: 9. A 75 kg object rests on a horizontal surface: a. The object s weight: Magnitude Direction: b. The surface s normal force: Magnitude Direction: c. Symbol: For Normal Force: Net Force: These are similar. But can you see the difference? d. Net force on the 75 kg object:. The forces are and the object is in. It doesn t. 10. When an object slides over a surface we have a pair of surfaces: The bottom of the and the itself. 11. Do all pairs of surfaces display the same amount of friction?. What constants indicate the amount of a pair s friction? 12. Provide the coefficients of friction for these surface pairs: Surface 1 Surface 2 s k Copper Steel Zinc Steel Aluminum Cast Iron 13. Liam uses a winch to exert 3,100 N of force to pull a 300 kg block with a rubber bottom over a dry cement floor. F N = f s = Will the block move? f k = a = 14. 1,345 N is required get a 225 kg resting on a surface moving. What is coefficient of static friction?. What is the surface pair?

7 Physics, Mr. Kent Daily Worksheet: Friction #2 Name: 1. Friction is a that motion. If a force is exerted South on an object then friction is exerted 2. A person pushes a box across a garage floor. Object exerting the push:. Object exerting the frictional force: 3. There are 2 types of friction. If an object is stationary on a surface, that surface exerts ( ). If an object is sliding over a surface (is moving) then the surface exerts ( ). Which of these frictions is larger?. That matches your experience, right? It s harder to an object moving than it is to it moving. 4. An object resting on a horizontal surface exerts a force down on the surface. The best name for that force:. The surface exerts a force up called the which is equal to. The forces are, the object is in and it does not. 5. of tell you how much friction exists between a of. The greek letter ( ) is used for these coefficients. a. Stationary objects:, b. Moving objects:, 6. Formula, Static Friction: Kinetic Friction: 7. A 4.5 kg block of glass is pushed over a copper surface with a force of 70 N. F N = f s = Will the block move? f k = F Net while moving? Acceleration? 8. In this formula, which variables on the right are variable and which is/are constant: f s = µ s m g So, what 2 factors affect friction? and

8 9. Complete this table to describe the difference surfaces/different masses demo: Surface 1 Surface 2 Mass f s f k 10. We ve already broken friction down between Static and Kinetic Frictions. There s another way to break friction down: Between & friction. is always greater. 11. Complete this table to describe the sliding vs. rolling friction demo. Description Kinetic Friction 12. Both and friction opposes you when you push a car from rest. Obviously, the tires along the road have friction. But inside the car, many surfaces over each other. In fact, most of the friction opposing you when you push a car from rest is.

9 Physics, Mr. Kent Name: Working Friction Quiz 1. Julien (75 kg) stands on a horizontal surface. Draw a free body diagram for Julien. Label each arrow with the name of the force and its magnitude. 2. A 150 kg cast iron block sits at rest on a horizontal copper surface. f s = f k = How much force must exerted: To move the object: To keep the block moving once it is in motion? 3. A force of 1,700 N is exerted on the block of problem #2. Will the block move? If so, what is the net force on the block while it s moving? At what rate will the block accelerate? 4. A force of 150 N is used to move a 15 kg block of steel over a steel surface. How far will the block move in 40 seconds? At what velocity will it be travelling at that time? 5. Robert exerts a force of 200 N on a 40 kg block of unknown substance on a surface of unknown substance causing it to accelerate at m/s 2. What is the net force exerted on the object while it s moving?. f k = µ k = What is the pair of surfaces?