Download PHYSICS Dynamics LESSON OBJECTIVES Students will be able to

PHYSICS
Dynamics
LESSON OBJECTIVES
Students w ill be able to...
define force
describe Newton’s First Law of Motion using inertia
identify the criteria of balanced and unbalanced forces
distinguish among net, applied and oppositional forces
describe Newton’s Second Law of Motion with respect to an unbalanced force
understand that force is the cause of acceleration
understand that grav ity is an attractiv e force between two masses
differentiate between mass and w eight
identify forces acting on a body that contribute to or hinder its motion
apply v ector resolution to a force acting perpendicularly
identify characteristics of friction and normal force
describe Newton’s Third Law of Motion
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SKILLS
Students w ill be able to...
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use appropriate metric units for giv en measurements
use steps for solv ing physics problems
draw free body diagrams
solv e problems using mass, acceleration and force, including gravity
conduct experiments relating to force and motion
collect and display experiment data
dev elop models of motion and force
VOCABULARY:
acceleration
force
mass
balanced force
unbalanced force
net force
grav ity
w eight
air resistance
inertia
friction
normal force
applied force
static friction
coefficient of friction
New ton (N)
deriv ed unit
HOMEWORK ASSIGNMENTS
Newton's First Law of Motion
#1: New ton's First Law, reading and homework page 1
#2: I nertia and Mass, reading and homework page 2
#3: State of Motion, reading
#4: Balanced and Unbalanced Forces, reading and homework pages 3-4
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Force and Its Representation
#5: The Meaning of Force, reading
#6: Types of Forces, reading and homework pages 5-9
#7: Draw ing Free-Body Diagrams, reading and homework page 10
#8: Determining the Net Force, reading and homework page 11-12
Newton's Second Law of Motion
#9: New ton's Second Law, reading and homework page 13
#10: The Big Misconception, reading
#11: Finding Acceleration, reading and homework page 14-17
#12: Finding I ndividual Forces, reading and homework page 18
Newton's Third Law of Motion
#13: New ton's Third Law , reading homework page 19-22
#14: I dentifying Action and Reaction Force Pairs, reading and homework page 23-24
CONTENT OUTLINE
I . New ton’s First Law of Motion
A. Mass and I nertia
B. Combining Forces
1. Balanced Forces
2. Unbalanced Forces
I I . Nature of Force
A. Definition
B. Types
1. Friction
a. Factors Affecting Gravity
b. Static and Dynamic Friction
2. Grav ity
a. Factors Affecting Gravity
i. mass
ii. distance
b. Weight v s. Mass
3. Other
C. Free Body Diagrams
D. Net Force
I II. Newton’s Second Law of Motion
A. Calculations
B. Using Free Body Diagrams
I V. Newton’s Third Law of Motion
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Newton’s First Law of Motion
1. When serving in v olleyball, the act of striking the ball is an example of applying
a. a pushing force
c. no force at all
b. a pulling force
d. both a pushing and pulling force
2.
A person w eighs less at the top of a mountain than at the base of a mountain because
a. a person has less mass at the top of a mountain
b. a person has more mass at the top of a mountain
c. a person is farther from the center of Earth w hen at the top of a mountain
d. there is less air pressure at the top of the mountain
3.
The force of 1 pound is equal to 4.5 new tons and the force of 1 kilogram is equal to 9.8
new tons. Which force is greater?
a. 10 pounds
b. 10 kg
c. 10 new tons
d. 50 new tons
A thrown baseball will move in a straight line at a constant speed (called uniform motion) until
another force affects it. The application of other forces will cause the ball to eventually slow
and stop.
4. What force does arrow 1 represent?
5. What force does arrow 2 represent?
6. Name another force that could also slow the ball and/or stop its motion.
Roberto threw a softball up into the air. It reaches a height of 9 meters
and then started to come down. He then threw the ball to a height of 12
meters.
7. What force pulled the ball dow n?
8. What is the most likely reason that the ball w ent higher on Roberto’s
second throw ?
9. What tw o conditions are necessary for uniform motion?
10. What is a force?
11. How is a force described?
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12. I n a diagram, one force arrow is longer than the other arrow. What can you tell about the
forces?
13. How can you find the net force if tw o forces act in opposite directions?
14. How do balanced forces acting on an object affect its motion? How do unbalanced forces
acting on an object affect its motion?
15. You exert a force of 120 N on a desk. Your friend exerts a force of 150 N in the same
direction. What net force do you and your friend exert on the desk?
16. Terrance helped his dad push their car out of the garage to repair it. He pushed as hard as
he could, but the car only mov ed v ery slowly. This example demonstrates the principle that
a. A body at rest remains at rest unless a force affects it.
b. A body in motion remains in motion unless a force affects it
c. A large mass requires a large force to mov e it
d. Ev ery action has an equal but opposite reaction
17. On a breezy day, Esther pushed her model sailboat across the still w ater in a pond.
According to New ton’s first law, the sailboat should hav e continued across the pond and
landed at Point A. How ever, it landed at Point B. The most likely reason for this w as that
a. the force of the w ind changed the sailboat’s direction of motion
b. fish sw imming near the sailboat changed its direction of motion
c. the force of the mov ing w ater changed the sailboat’s direction of motion
d. the sailboat accelerated across the pond
18. What is the relationship betw een the mass and inertia of an object?
a. the greater the mass, the greater the inertia
b. the greater the mass, the less the inertia
c. the less the mass, the greater the inertia
d. the mass and the inertia are not related
19. Which of the follow ing objects w ould need the greatest force to be stopped?
a. a baseball mov ing at 80 km/hr
c. a train mov ing at 80 km/hr
b. a car mov ing at 80 km/hr
d. an arrow moving at 80 km/hr
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Gail and Jared set up an experiment that they read about in their science textbook which used
a glass, sev eral coins (penny, nickel, and quarter), and an index card. The students flicked the
card from under each of the coins to see w hat w ould happen.
20.
When they flicked the card from
under each of the coins,
a. the coins all stayed w ith the card and fell
on the table
b. the coins all dropped into the glass
c. the quarter fell into the glass, and the
other tw o coins fell on the table
d. the penny fell into the glass, and the
other tw o coins fell on the table
21. This experiment indicated that an object at rest w ill remain at rest and w ill resist being put
into motion. What term best expresses what this experiment demonstrated?
a. differences in mass
c. inertia
b. acceleration
d. differences in motion
22. The quarter has the greatest mass of the three coins. Therefore, it w ould hav e the greatest
a. resistance to change in motion
c. change in direction
b. acceleration
d. distance to fall
23. Explain w hy a lead ball 5 cm in diameter has more inertia than a w ooden ball 5 cm in
diameter.
24. What does New ton’s 1st Law say?
25. I f you hold a coin abov e (and a tiny bit to the side of) your head w hile standing in a bus
that is not mov ing, the coin w ill land at our feet w hen you drop it. Where w ill it land if the
bus is mov ing in a straight line at constant speed? Why?
26. Your brain is not attached by any tissue to your skull, it simply floats inside. A concussion
happens w hen your brain hits the inside of your skull and gets bruised or damaged. Use
New ton’s first law to explain w hat happens w hen you get a concussion by running into a
w all.
Friction and Gravity
27. What factors affect the friction force between two surfaces?
28. What is the law of univ ersal gravitation?
29. How do mass and distance affect the grav itational attraction between objects?
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30. How w ould your weight change on the surface of an Earth-sized planet w hose mass w as
greater than Earth’s? Why?
31. Why does an object accelerate when it falls tow ard Earth’s surface?
32. How does the mass of an object affect its acceleration during free fall?
33. Which of the four different balls listed w ould require the greatest force to mov e?
a. golf ball
c. bow ling ball
b. baseball
d. basketball
34. The mass of the stature of liberty w ould be
a. greatest in NYC
b. greatest at the north pole
c. greatest at the moon
d. the same in all locations
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35. A w oman w eighs 580 N. What is her mass?
36. Find the w eight of a 2000 kg elephant.
37. An astronaut has a mass of 85 kg. Calculate his w eight on Earth and on the Earth’s moon
(gmoon = 1.6 m/s2). Does his mass change w hen he goes from Earth to its moon?
38. Calculate the w eight of a 4.5 kg rabbit.
39. At the surface of Mars the acceleration due to gravity is 3.8 m/s2. A book w eighs 34 N at the
surface of the Earth. What is its mass on the earth’s surface? What are its mass and w eight
on Mars’s surface?
40. A boy w eighs 270 N. What is his mass?
41. Find the w eight of a 60 kg table.
42. A Martian w eighs 17 N on the surface of Mars. Calculate his w eight on Earth and on the
Earth’s moon. Does his mass change along the flight from Mars to the Moon to the Earth?
The acceleration due to gravity on Mars is 3.8 m/s2 and the acceleration due to grav ity on
the Moon is 1.6 m/s2.
43. Find the w eight of a 2 g computer chip.
44. What is the mass of a 330 N telev ision?
45. The mars rov er, Spirit has a mass of 836 kg. Calculate its w eight on Earth and on Mars. The
acceleration due to grav ity on Mars is 3.8 m/s2
Newton’s Second Law
46. How could you keep an object’s acceleration the same if the force acting on the object
w ere doubled?
47. Using w hat you know about Newton’s second law, explain w hy a car w ith a large mass
might use more fuel than a car w ith a smaller mass. Assume both cars driv e the same
distance.
48. Find the force it w ould take to accelerate an 800-kg car at a rate of 5 m/s2.
49. What is the net force acting on a 0.15-kg hockey puck accelerating at a rate of 12 m/s2?
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50. How much force is needed to accelerate a 68 kilogram-skier at a rate of 1.2 m/sec2?
51. What is the mass of an object that requires a force of 30 N to accelerate at a rate of 5
m/sec2?
52. What is the force on a 1,000 kilogram-elevator that is falling freely under the acceleration of
grav ity only?
53. What is the mass of an object that needs a force of 4,500 N to accelerate it at a rate of 5
m/sec2?
54. What is the acceleration of a 6.4 kilogram bow ling ball if a force of 12 N is applied to it?
55. According to New ton’s second law, an increase in force on a giv en mass w ill cause:
a. a decrease in acceleration
c. a decrease in the mass
b. an increase in acceleration
d. an increase in the mas
56. A rocket traveling in space increases its v elocity from 32,000 km/hr to 40,000 km/hr. To do
this, the rocket must
a. increase its mass
c. increase the force acting on it
b. decrease its mass
d. decrease the force acting on it
57. A 0.40 kg toy car mov es at constant acceleration of 2.3 m/s2. Determine the net applied
force that is responsible for that acceleration.
58. I f a net horizontal force of 175 N is applied to a bike w hose mass is 43 kg w hat
acceleration is produced?
59. What av erage net force is required to stop a 7 kg shopping cart in 2 s if it’s initially
trav eling at 3.5 m/s?
60. A 7.5 kg cannon ball leav es a canon w ith a speed of 185 m/s. Find the av erage net force
applied to the ball if the cannon muzzle is 3.6 m long.
61. A w ooden block is pulled at a constant acceleration of 1.4 m/s2. Find the net applied
force on the block if its mass is 0.6 kg.
62. A 95 N net force is applied to an ice block w ith a mass of 24 kg. Find the acceleration of
the block if it mov es on a smooth horizontal surface.
63. A net force of 345 N accelerates a boy on a sled at 3.2 m/s2. What is the combined mass
of the sled and boy?
64. What av erage net force is required to stop an 8500 kg truck in 10 s if it’s initially trav eling at
20 m/s?
65. What av erage net force is required to accelerate a 9.5 g bullet from rest to 650 m/s ov er
a distance of 0.85 m along the barrel of a rifle?
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66. A physics student pushed a 50 kg load across the floor, accelerating it at a rate of 1.5
m/s2. How much force did she apply?
67. A 10,000 N net force is accelerating a car at a rate of 5.5 m/s2. What is the car’s mass?
68. A boy pedals his bicycle w ith a net horizontal force of 235 N. I f the total mass of the boy
and the bike is 40 kg, how much are they accelerating?
69. A 45 kg sw immer starting from rest can dev elop a maximum speed of 12 m/s ov er a
distance of 20 m. How much net force must be applied to do this?
70. A net force of 3000 N is accelerating a 1200 kg elev ator upward. If the elevator starts from
rest, how long w ill it take to trav el up 15 m?
71. A 57 kg paratrooper falls through the air. How much force is pulling him dow n?
72. A net force of 34 N is applied to accelerate an object at a rate of 2.5 m/s2. What is the
mass of the object?
73. A runner exerts a net force of 225 N to accelerate at a rate of 3.0 m/s2. What is the
runner’s mass?
74. What av erage net force is required to stop a 4 kg bow ling ball in 0.5 s if it’s initially
trav eling at 10 m/s?
75. A hockey puck w ith a mass of 0.18 kg is at rest on the horizontal frictionless surface of the
rink. A player applies a horizontal force of 0.5 N to the puck. Find the speed and the
trav eled distance 5 s later.
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Newton’s Third Law
The third law of motion states that for ev ery action there is an equal and opposite reaction.
A simple demonstration of blow ing up a balloon and letting it go show s how this law works.
When the air is released from an opening in the balloon, the balloon mov es in the opposite
direction. Other actions that produce and equal and opposite reaction force include
kicking a soccer ball, w aling, and hot gas shooting out of a rocket engine.
76. According to New ton’s third law of motion, how are action and reaction forces related?
77. What w ould happen if you tried to catch a ball w hen you w ere standing on roller skates?
78. A CO2 cartridge w as mounted on the top of a toy car w ith the nozzle of the cartridge
pointing tow ard the rear of the car. When the compressed gas w as released from the
cartridge, the toy car mov ed 6 meters across the room and stopped. What can be
changed so that the car w ill travel a shorter distance?
79. The third law of motion states that for ev ery action there is an equal and opposite
reaction. A simple demonstration of blow ing up a balloon and letting it go show s how this
law w orks. When the air is released from an opening in the balloon, the balloon mov es in
the opposite direction. Other actions that produce and equal and opposite reaction
force include kicking a soccer ball, w aling, and hot gas shooting out of a rocket engine.
80. According to New ton’s third law of motion, how are action and reaction forces related?
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Free body diagrams
Coefficient of Friction:
Symbol
FN
FW
Ffr
Fa
µ
Meaning an unit
FN=Fw
Ffr = µFN
81. A box sits at rest on a tabletop. Draw and clearly label all the forces acting on the box;
compare their magnitudes and directions.
82. A w ooden block mov es at a constant speed on a rough horizontal surface. Draw a freebody diagram clearly showing all the forces applied to the block; compare their
magnitudes and directions.
83. A crane lifts a load at a constant speed. Draw a free-body diagram for the load and
compare the magnitudes and directions of the all forces.
84. A crate is accelerated at a constant rate along a rough horizontal floor. Draw a freebody diagram for the crate and compare all the forces exerted on the crate.
85. A hockey puck slides on a rough horizontal surface. Draw a free-body diagram for the
puck and compare the magnitudes and the directions of all the forces exerted on it.
86. A boy pulls a sled horizontally at a constant speed by holding a rope that is connected to
the sled.
a. Show all the forces exerted on the sled (do not ignore friction);
b. Show all the forces exerted on the boy (do not ignore friction);
c. Show all the forces acting on the rope;
d. Use New ton’s Law to explain the directions and the magnitudes of all the forces;
compare “action” and “reaction”.
87. A hockey puck has a coefficient of kinetic friction of μk = .10. I f the puck feels a normal
force (FN) of 5.0 N, w hat is the frictional force that acts on the puck?
88. Suppose a 10.0 N force is applied to the side of a 4.0 kg block that is sitting on a table.
The block experiences a frictional force against the force that is applied.
a. Draw a force diagram for the block.
b. What is the w eight of the block (Fw )?
c. What is the normal force on the block (FN)?
d. I f the coefficient of friction is μ = .20, w hat is the frictional force on the block (Ff)?
e. What is the net force on the block?
f. What is the acceleration of the block from the net force?
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89. For the block in Problem 2, w hat w ould be the minimum v alue of the coefficient of static
friction in order for the block to remain motionless?
90. A block w eighing 300.0 N is mov ed at a constant speed ov er a horizontal surface by a
force of 50.0 N applied parallel to the surface. What does the “constant speed” tell you
about the forces acting on the block?
a. Draw a force diagram for the block.
b. What is the coefficient of kinetic friction (μk)?
c. What is the mass of the block?
d. What w ould be the acceleration of the block if μ = 0.0?
91. A 100. N force is applied to the side of a crate resting on a lev el floor. The crate has a
mass of 50. kg. I f the coefficient of static friction is μ = .25, is the 100. N force enough to
make the crate accelerate? Explain w hy or w hy not. (As alw ays, start w ith a force
diagram)
92. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.25. The w eight of the object is 20N. What is the force of friction?
93. The force of friction between an object and the surface upon w hich it is sliding is 12N. The
w eight of the object is 20N. What is the coefficient of kinetic friction?
94. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.40. The mass of the object is 3.2 kg. What is the force of friction?
95. The force of friction between an object and the surface upon w hich it is sliding is 15N. The
mass of the object is 20kg. What is the coefficient of kinetic friction?
96. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.40. The w eight of the object is 80N. What is the force of friction?
97. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.6. The mass of the object is 12 kg. What is the force of friction?
98. The force of friction between an object and the surface upon w hich it is sliding is 12N and
the coefficient of friction between them is 0.70. What is the w eight of the object?
99. The force of friction between an object and the surface upon w hich it is sliding is 250N
and the coefficient of friction between them is 0.80. What is the mass of the object?
100. The force of friction between an object and the surface upon w hich it is sliding is 36N.
The w eight of the object is 85N. What is the coefficient of kinetic friction?
101. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.10. The mass of the object is 8.0 kg. What is the force of friction?
102. The force of friction between an object and the surface upon w hich it is sliding is 46N
and the coefficient of friction between them is 0.30. What is the w eight of the object?
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103. The force of friction between an object and the surface upon w hich it is sliding is 360N.
The mass of the object is 95kg. What is the coefficient of kinetic friction?
104. The force of friction between an object and the surface upon w hich it is sliding is 126 N
and the coefficient of friction between them is 0.20. What is the mass of the object?
105. The force of friction between an object and the surface upon w hich it is sliding is 12 N
and the coefficient of friction between them is 0.60. What is the w eight of the object?
106. The coefficient of kinetic friction between an object and the surface upon w hich it is
sliding is 0.15. The mass of the object is 16kg. What is the force of friction?
107. The force of friction between an object and the surface upon w hich it is sliding is 3.5N.
The mass of the object is 4 kg. What is the coefficient of kinetic friction?
108. The force of friction between an object and the surface upon w hich it is sliding is 100 N
and the coefficient of friction between them is 0.24. What is the mass of the object?
109. A stationary 15 kg object is located on a table near the surface of the earth. The
coefficient of static friction between the surfaces is 0.40 and the coefficient of kinetic
friction is 0.25. A horizontal force of 20 N is applied to the object.
a. Draw a free body diagram w ith the forces to scale,
b. Determine the force of friction,
c. Determine the acceleration of the object,
d. Now a horizontal force of 40 N is applied to the object.
e. Draw a free body diagram w ith the forces to scale.
f. Determine the force of friction.
g. Determine the acceleration of the object.
h. Now a horizontal force of 60 N is applied to the object.
e. Draw a free body diagram w ith the forces to scale.
j. Determine the force of friction.
k. Determine the acceleration of the object.
l. Now a horizontal force of 100 N is applied to the object.
m. Draw a free body diagram w ith the forces to scale.
n. Determine the force of friction.
o. Determine the acceleration of the object.
110. A stationary 250 kg object is located on a table near the surface of the earth. The
coefficient of static friction between the surfaces is 0.30 and the coefficient of kinetic
friction is 0.15. A horizontal force of 300 N is applied to the object.
a. Draw a free body diagram w ith the forces to scale.
b. Determine the force of friction.
c. Determine the acceleration of the object?
d. A horizontal force of 1500 N is applied to the object.
e. Draw a free body diagram w ith the forces to scale.
f. Determine the force of friction.
g. Determine the acceleration of the object.
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111. A stationary 2.0 kg object is located on a table near the surface of the earth. The
coefficient of static friction between the surfaces is 0.80 and the coefficient of kinetic
friction is 0.65. A horizontal force of 5 N is applied to the object. Repeat a-c for the
application of a 20 N force.
a. Draw a free body diagram w ith the forces to scale.
b. Determine the force of friction.
c. Determine the acceleration of the object.
112. A 1500 kg elev ator mov es up and dow n on a cable. Calculate the tension in the
cable for the follow ing cases:
a. The elev ator mov es at constant speed upw ard
b. The elev ator mov es at constant speed downward
c. The elev ator accelerates upward at a constant rate of 1.2 m/s2
d. The elev ator accelerates downward at a constant rate of 1.2 m/s2
113. A crane accelerates a 175 kg load is upw ard. The tension in the cable is 2000 N. Find
the magnitude and direction of the elev ator’s acceleration.
114. A 65 kg w oman is inside an elev ator. Calculate her apparent weight for the following
cases:
a. The elev ator mov es at constant speed upw ard
b. The elev ator mov es at constant speed downward
c. The elev ator accelerates upward at a constant rate of 2.4 m/s2
d. The elev ator accelerates downward at a constant rate of 2.4 m/s2
115. An 800 N man stands on a scale in a motionless elev ator. When the elevator begins to
mov e, the scale reads 650 N. Find the magnitude and direction of the elev ator’s
acceleration.
116.
a.
b.
c.
d.
117.
a.
b.
c.
d.
e.
A train w ith a mass of 25000 kg increases its speed from 10 m/s to 25 m/s in 20 seconds.
Assume that the acceleration is constant and that you can neglect friction.
Find the acceleration of the train
Find the distance trav eled during this 20 s?
Draw a free- body diagram for the train;
Find the av erage net force supplied by the locomotiv e.
A 150 kg motorcycle starts from rest and accelerates at a constant rate along a
distance of 350m. The applied force is 250 N and the coefficient of kinetic friction is
0.03.
Draw a free-body diagram for the motorcycle showing all applied forces to scale.
Next to that diagram show the direction of the acceleration;
Find the net force applied to the motorcycle;
Find the acceleration of the motorcycle;
What is its speed at the end of 350 m?
Find the elapsed time of this acceleration.
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Directions: For each of the following, write the letter of the choice that best completes the
sentence.
118.
When you exert a force on an object it exerts ______ force back on you.
a. a stronger
b. the same
119.
When v olleyball players jump into the air, the primary force acting to make them land
back on the ground is ______.
a. mass
b. grav ity
120.
Forces alw ays act in ______.
a. pairs
b. singles
121.
I n a game of tug-o-w ar, the team that w ins has exerted a greater ______ force.
a. unbalanced
b. mass
122.
When you are pushing on a large door, ______ friction keeps you from sliding
backw ards.
a. unbalanced
b. static
123.
______ is determined by grav ity.
a. w eight
b. mass
124.
A component of inertia is ______.
a. mass
b. friction
125.
______ friction causes a car tire to turn on the road.
a. Static
b. Rolling
126.
______ friction keeps an object from mov ing w hen a force is applied.
a. Static
b. Sliding
127.
I f the same force is applied to tw o different objects, the one w ith the ______ mass has
a smaller acceleration.
a. larger
b. smaller
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