Directed Reading B Section: Friction: A Force That Opposes Motion Circle the letter of the best answer for each question.
1. What unbalanced force causes a ball to stop rolling? a. friction opposing motion b. gravity pulling down c. the ground pushing up d. the force of the throw or kick THE SOURCE OF FRICTION 2. What two things affect the amount of friction? a. energy and heat b. energy and surface roughness c. force and heat d. force and surface roughness The Effect of Force on Friction
3. Why does sliding large books take more force than sliding small books? a. The large books have more surface roughness. b. The large books have more weight pushing down. c. The large books have less air. d. The large books have less heat. The Effect of Rougher Surfaces on Friction
Directed Reading B continued Circle the letter of the best answer for each question.
5. What happens to the road friction when a road gets rougher? a. There is no friction. b. The friction is less. c. The friction is greater. d. The amount of friction stays the same. TYPES OF FRICTION Kinetic Friction
6. Which of these examples shows sliding kinetic friction? a. pushing a desk across the floor b. pushing a desk that will not move c. a bicycle on a sidewalk d. an airplane flying 7. Which of these examples shows rolling kinetic friction? a. pushing a desk across the floor b. pushing a desk that will not move c. a bicycle moving on a sidewalk d. an airplane flying Static Friction
8. Which of these examples shows static friction? a. pushing a desk across the floor b. pushing a desk that will not move c. a bicycle on a level sidewalk d. an airplane flying
Directed Reading B continued Circle the letter of the best answer for each question.
9. Which kind of friction keeps a heavy object from moving when you push it? a. rolling kinetic friction b. sliding kinetic friction c. static friction d. surface friction 10. Which type of friction occurs once an object is moving? a. no friction b. kinetic friction c. static friction d. surface friction Read the description. Then, draw a line from the dot next to each description to the matching word.
• • •
11. a hockey puck moving on ice 12. a crate resting on a ramp 13. a car racing in competition
a. sliding kinetic friction b. rolling kinetic friction c. static friction
Directed Reading B continued Use the figures below to answer questions 14, 15, and 16. Circle the letter of the best answer for each question.
Block
Force applied
Static friction
Force applied
Kinetic friction
Table
(A)
(B)
(C)
14. Look at Figure A above. Why does the block not move? a. no force is being applied b. force of friction c. surface friction d. kinetic friction 15. Look at Figure B above. The block does not move. What force keeps the block from moving? a. rolling kinetic friction b. sliding kinetic friction c. static friction d. kinetic friction 16. Look at the Figure C above. The block is moving. What force acts against the block’s motion? a. static friction b. sliding kinetic friction c. rolling kinetic friction d. gravity
FRICTION: HARMFUL AND HELPFUL Circle the letter of the best answer for each question.
17. What would happen if you tried to walk without friction? a. you would slip and fall b. you would get lost c. you would change direction d. you would go slower Some Ways to Reduce Friction
18. Which of the following is a way to reduce friction? a. Wear textured batting gloves. b. Press harder while sanding wood. c. Increase the force between two surfaces. d. Place ball bearings between wheels and axles. Some Ways to Increase Friction
19. Which of the following is a way to increase friction? a. Use a lubricant. b. Make rubbing surfaces smoother. c. Push surfaces together. d. Switch sliding kinetic friction to rolling kinetic friction.
direction direction same opposite acceleration accelerating increasing decreasing C B A D
SECTION: WHAT IS A FORCE? 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
force motion newton B C B D A A D A B B
SECTION: FRICTION: A FORCE THAT OPPOSES MOTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
A D B D C A C B C B A C B A C B A A B
SECTION: GRAVITY: A FORCE OF ATTRACTION 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
A A C D B A B Earth planet force gravitation C D A B C D B D A B
Vocabulary and Section Summary SECTION: MEASURING MOTION 1. motion: an object’s change in position
relative to a reference point 2. speed: the distance traveled divided by
the time interval during which the motion occurred 3. velocity: the speed of an object in a particular direction 4. acceleration: the rate at which velocity changes over time; an object accelerates if its speed, direction, or both change
SECTION: WHAT IS A FORCE? 1. force: a push or a pull exerted on an
object in order to change the motion of the object; force has size and direction 2. newton: the SI unit for force (symbol, N) 3. net force: the combination of all of the forces acting on an object
