Reviewing Main Ideas
1
Newton’s First Law
• A force is a push or a pull.
• Newton’s first law states that objects in
motion tend to stay in motion and objects at
rest tend to stay at rest unless acted upon by
a net force.
• Friction is a force that resists motion between
surfaces that are touching each other.
Reviewing Main Ideas
2
Newton’s Second Law
• Newton’s second law states that an object
acted upon by a net force will accelerate in
the direction of this force.
• The acceleration due to a net force is given
by the equation a = Fnet/m.
Reviewing Main Ideas
2
Newton’s Second Law
• The force of gravity between two objects
depends on their masses and the distance
between them.
• In circular motion, a force pointing toward
the center of the circle acts on an object.
Reviewing Main Ideas
3
Newton’s Third Law
• According to Newton’s third law, the forces
two objects exert on each other are always
equal but in opposite directions.
• Action and reaction forces don’t cancel
because they act on different objects.
• Objects in orbit appear to be weightless
because they are in free fall around Earth.
Chapter Review
Question 1
Which of Newton’s laws
explains how this rocket
gets off the ground?
IN: 7.3.17
Chapter Review
Answer
Newton’s third law explains how a rocket
moves upward. The force of the propellant
being driven out the base of the rocket causes
an equal but opposite force pointing in the
other direction, which drives the rocket up.
IN: 7.3.17
Chapter Review
Question 2
When the air resistance force equals a falling
object’s weight, the net force on the falling
object is zero. The object has reached _______.
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Chapter Review
Answer
The answer is terminal velocity. This means its
acceleration is zero; it does not mean that the
falling object stops moving.
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Chapter Review
Question 3
If you are going around in circles, even at an
unchanging speed, you are constantly _______.
A. accelerating
B. increasing in velocity
C. increasing your distance
D. slowing down
IN: 7.3.17
Chapter Review
Answer
The answer is A. This is called circular motion.
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Chapter Review
Question 4
When you throw a ball, why doesn’t it move in
a straight line?
Answer
It would, if you were in space. On Earth,
however, the force of gravity causes it to move
in a curve as it falls.
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Chapter Review
Question 5
What is responsible for slowing down the lunch
trays in this illustration?
A. acceleration
B. friction
C. gravity
D. inertia
IN: 7.3.17
Chapter Review
Answer
The answer is B. Friction always opposes
sliding between two objects.
IN: 7.3.17
Standardized Test Practice
Question 1
Which would remain unchanged were you to go
up in the space shuttle?
A. your distance from the Earth
B. your mass
C. your perceptions
D. your weight
IN: 7.3.17
Standardized Test Practice
Answer
The answer is B. Your weight is relative to
your distance from Earth and whether or not
you are in freefall.
IN: 7.3.17
Standardized Test Practice
Question 2
You are swimming laps in a pool. When you
come to the end, you turn around underwater
and push off the wall. What does the wall do?
A. it changes state
B. it does nothing
C. it pushes back
D. it pulls on you
IN: 7.3.17
Standardized Test Practice
Answer
The answer is C. Newton’s third law states
that the wall pushes back on you with the
same amount of force you exert on it.
IN: 7.3.17
Standardized Test Practice
Question 3
Suppose you are in a space station when
suddenly you realize an asteroid is headed
your way. What do you need to know
about the asteroid to know how forceful
the impact will be?
IN: 7.3.17
Standardized Test Practice
A. its mass
B. its acceleration
C. its mass and its acceleration
D. its mass and its acceleration and its origin
IN: 7.3.17
Standardized Test Practice
Answer
The correct answer is C. Newton showed that
f =ma. If the asteroid is moving very slowly,
or if it has very little mass, the force of its
impact will be much less than if it is very
massive and moving quickly.
IN: 7.3.17
Standardized Test Practice
Question 4
Which object would have the least acceleration
if you pushed on it with a force of 5 N?
A. book
B. can
C. cup
D. stapler
Object
Mass (g)
Cup
380
Book
1,100
Can
240
Ruler
25
Stapler
620
IN: 7.3.17
Standardized Test Practice
Answer
The answer is A. Acceleration is calculated
using the equation a = Fnet/m.
IN: 7.3.17
Standardized Test Practice
Question 5
The type of friction that prevents an object from
starting to move is known as _______.
A. static electrical friction
B. static friction
C. typical friction
D. total friction
IN: 7.3.17
Standardized Test Practice
Answer
The answer is B. Static friction is different
from sliding friction, which slows down an
object that is sliding.
IN: 7.3.17