Chapters 2 & 3: Force,
Motion, & Newton’s Laws
Review
Physical Science
Glencoe Science © 2002
Speed
• The rate of change of position
• Speed = distance
time
• SI Units: cm/s, m/s, km/h
• A scalar quantity (has magnitude, but no
direction)
Total distance divided by total
time is:
A.
B.
C.
D.
Average speed
Constant speed
Variable speed
Instantaneous speed
Total distance divided by total
time is:
A.
B.
C.
D.
Average speed
Constant speed
Variable speed
Instantaneous speed
Constant Speed
• Does not vary
• Example?
Constant Speed
• Does not vary
• Example: CRUISE CONTROL
Instantaneous Speed
• The speed at any given ____.
Instantaneous Speed
• The speed at any given instant.
A man drives 3 km east from
home to the store and then 2 km
west to a friend’s house. What
is his displacement from his
starting point at home?
A.
B.
C.
D.
1 km west
1 km east
5 km west
5 km east
A man drives 3 km east from
home to the store and then 2 km
west to a friend’s house. What
is his displacement from his
starting point at home?
A.
B.
C.
D.
1 km west
1 km east
5 km west
5 km east
Acceleration
• The rate of change in velocity
• a = vf - vi = ∆v
tf - ti
∆t
The proper units of acceleration
are:
A.
B.
C.
D.
s/km2
km/h
m/s2
cm/s
The proper units of acceleration
are:
A.
B.
C.
D.
s/km2
km/h
m/s2
cm/s
Which of the following is NOT
used in calculating acceleration?
A.
B.
C.
D.
initial velocity
average speed
time interval
final velocity
Which of the following is NOT
used in calculating acceleration?
A.
B.
C.
D.
initial velocity
average speed
time interval
final velocity
In which of the following
conditions does the car NOT
accelerate?
A. A car moves at 80 km/h on a flat, straight
highway.
B. The car slows from 80 km/h to 35 km/h.
C. The car turns a corner.
D. The car speeds up from 35 km/h to 80 km/h.
In which of the following
conditions does the car NOT
accelerate?
A. A car moves at 80 km/h on a flat, straight
highway.
B. The car slows from 80 km/h to 35 km/h.
C. The car turns a corner.
D. The car speeds up from 35 km/h to 80 km/h.
A body accelerates if it_____.
a. speeds up
b. slows down
c. changes direction
d. all of these
A body accelerates if it_____.
a. speeds up
b. slows down
c. changes direction
d. all of these
A constant velocity means that
acceleration is ____.
A.
B.
C.
D.
E.
F.
positive
negative
increasing
decreasing
constant
zero
A constant velocity means that
acceleration is ____.
A.
B.
C.
D.
E.
F.
positive
negative
increasing
decreasing
constant
zero
Which of the terms below best
describe the forces on an object
with a net force of zero?
A.
B.
C.
D.
inertia
balanced forces
acceleration
unbalanced forces
Which of the terms below best
describe the forces on an object
with a net force of zero?
A.
B.
C.
D.
inertia
balanced forces
acceleration
unbalanced forces
The tendency of an object to
resist any change in its motion:
A.
B.
C.
D.
Net force
Acceleration
Balanced force
Inertia
The tendency of an object to
resist any change in its motion:
A.
B.
C.
D.
Net force
Acceleration
Balanced force
Inertia
Newton’s First Law of Motion
•
•
•
An object in motion stays in motion
and an object at rest stays at rest
unless acted upon by an unbalanced
force.
the resistance of an object to change
its motion
also known as the Law of Inertia
Which of the objects has the
greatest inertia?
A.
B.
C.
D.
a car parked on the side of the road
a baseball during a pop fly
a computer sitting on a desk
a woman running on a track
Which of the objects has the
greatest inertia?
A.
B.
C.
D.
a car parked on the side of the road
a baseball during a pop fly
a computer sitting on a desk
a woman running on a track
An object of large mass has
______ than an object of small
mass.
A.
B.
C.
D.
less inertia
more inertia
less weight
greater acceleration
An object of large mass has
______ than an object of small
mass.
A.
B.
C.
D.
less inertia
more inertia
less weight
greater acceleration
Which answer best describes
why a passenger who is not
wearing a seat belt will likely hit
the windshield in a head-on
collision?
A.
B.
C.
D.
forces acting on the windshield
inertia of the unbelted person
acceleration of car
gravity taking over
Which answer best describes
why a passenger who is not
wearing a seat belt will likely hit
the windshield in a head-on
collision?
A.
B.
C.
D.
forces acting on the windshield
inertia of the unbelted person
acceleration of car
gravity taking over
Newton’s 2nd Law of Motion
• A net force causes an • Units of Force=
2
Newtons
(N)
or
kg▪
m/s
object to accelerate in
the direction of the net • Units of Mass = kg
force.
• Units of accel. = m/s2
• Acceleration = Force
mass
 a = F/m
 m = F/a
 F = ma
Newton
• Unit of Force or weight
• 1 N = 1 kg▪ m/s2
A weightlifter raises a 440-kg
barbell with an acceleration
2
of 2.00 m/s . How much
force does the weightlifter
exert on the barbell?
A weightlifter raises a 440-kg barbell
with an acceleration of 2.00 m/s2.
How much force does the weightlifter
exert on the barbell?
F = ma
F = (440 kg)(2.00 m/s2)
F = 880 kg▪ m/s2 = 880 N
Friction
• Is caused by microwelds that develop
between the microscopic bumps on 2
surfaces.
• 3 types of friction: static, sliding, and
rolling
Acceleration due to Gravity
• All objects are attracted to Earth with
the same acceleration.
• Air resistance exerts an upward force
on objects falling through the
atmosphere
• Terminal velocity - when the force of air
resistance equals the force of gravity
and the falling object no longer
accelerates
The Law of Gravitation
• Anything that has mass is attracted by
the force of gravity.
• Any 2 masses exert an attractive force
on each other.
• The attractive force depends on the
mass of the 2 objects and the distance
between them.
4 Basic Forces
• Gravity
– a long-range force
– NEVER disappears
– Gravity is the force that gives a galaxy its
shape and the universe its structure
• Electromagnetic Force
• Strong nuclear force
• Weak nuclear force
Gravitational Acceleration
• Near Earth’s surface, the gravitational
attraction of the Earth causes all objects
to have an acceleration of 9.8 m/s2
• According to Newton’s 2nd Law, F = ma
• F = m x 9.8 m/s2
• The direction of gravitational force is
downward
• When an object is only under the force of
gravity, it is said to be in free-fall.
The gravitational force between
two objects depends on_______.
A.their masses
B.their velocities
C.their shapes
D.the distance between them
E.more than one of the above
(Which ones?)
The gravitational force between
two objects depends on_______.
A.their masses
B.their velocities
C.their shapes
D.the distance between them
E.more than one of the above
(A and D)
Weight
•
•
•
•
The gravitational force exerted on an object.
W = mg (same as F = ma)
W = mass (kg) x 9.8 m/s2
What is the difference between weight and
mass?
“Weightlessness” in space
• is caused by the orbiting space shuttle
falling downward, and no force is
pushing upward (remember, gravity is
also a downward force), so they seem
to be floating.
Projectile Motion
• Projectile - anything shot or thrown
through the air.
• Projectiles have both horizontal and
vertical motion
•
See http://www.batesville.k12.in.us/Physics/PhyNet/Mechanics/Projectiles/HorProPath.html
Centripetal Force
• Centripetal acceleration - acceleration toward
the center of a circular path
• Centripetal force - an unbalanced force
toward the center acting on an object moving
in a circular path.
•
SEE http://hyperphysics.phy-astr.gsu.edu/hbase/cf.html
•
ALSO SEE http://regentsprep.org/Regents/physics/phys06/bcentrif/default.htm
Newton’s 3rd Law of Motion
• Describes action - reaction pairs: when one
object exerts a force on a second object, the
second one exerts a force on the first that is
equal and opposite in direction.
• “to every action force there is an equal and
opposite reaction force.”
•
•
For a description of Newton’s 3 Laws of motion, see
http://csep10.phys.utk.edu/astr161/lect/history/newton3laws.html
More in depth: http://electron9.phys.utk.edu/phys135d/modules/m4/3rdLaw.htm
Rocket Propulsion
• Rocket releases gases, the gases push
back on the rocket in the opposite
direction.
•
http://www.glenbrook.k12.il.us/GBSSCI/PHYS/CLASS/newtlaws/u2l4a.html
Momentum
• P=mxv
• Units are kg x m/s
• Do not confuse this
with F = ma
= kg x m/s2 or
Newtons
See: http://www.glenbrook.k12.il.us/gbssci/phys/Class/momentum/u4l2e.html
Law of Conservation of
Momentum
• The momentum of an object does not
change unless its mass, velocity, or
both change.
• If a group of objects exerts forces only
on each other, their total momentum
does not change.
• m1v1 = m2v2
Answers to the Chapter 3 Study
Guide and Assessment (p. 95-97)
•
•
•
•
•
•
•
page 95
1. c. friction
2. a. centripetal acceleration
3. g. Newton’s 3rd Law of Motion
4. h. weight
5. e. momentum
6. f. Newton’s 2nd Law of Motion
1. What will happen to an object
when a net force acts on it?
a)
b)
c)
d)
Fall
Stop
Accelerate
Go in a circle
Answer: C
2. Which is Newton’s 2nd law?
•
•
•
•
A) F = ½ ma2
B) F = 2 ma
C) p = mv
D) a = F/m
• Answer: D
3. The force of gravity on an
object is known as ___.
•
•
•
•
A) centripetal force
B) friction
C) momentum
D) weight
• Answer: D
4. Which of the following is NOT
a type of friction?
•
•
•
•
A. static
B. sliding
C. centripetal
D. rolling
• Answer: C
5. What is true about an object
falling toward Earth?
•
•
•
•
A. It falls faster the heavier it is.
B. It falls faster the lighter it is.
C. Earth pulls on it, and it pulls on Earth
D. It has no weight.
• Answer: C
6. Why do projectiles follow a
curved path?
• A. They have a horizontal and a vertical
motion.
• B. They have centripetal force.
• C. They have momentum.
• D. They have inertia.
• Answer: A
7. The product of mass and
velocity is known as:
•
•
•
•
A. gravity
B. momentum
C. friction
D. weight
• Answer: B
8. Which body exerts the weakest
gravitational force on Earth?
•
•
•
•
A. the Moon
B. Mars
C. Pluto
D. Venus
• Answer: C
9. When a leaf falls, what force
opposes gravity?
•
•
•
•
A. air resistance
B. terminal velocity
C. friction
D. weight
• Answer: A
10. In circular motion, the centripetal
force is in what direction?
•
•
•
•
A. forward
B. backward
C. toward the center
D. toward the side
• Answer: C
11. What is the weight on Earth of a
person with a mass of 65 kg?
• Solution:
Use F = ma; therefore W = mg
(W = weight in Newtons; g = 9.8 m/s2)
W=mg
W = (65 kg)(9.8 m/s2)
W = 637 N
12. Some people put chains on
their tires in the winter. Why?
Answer:
• The chains help provide traction on the
ice and snow by increasing the amount
of friction between the tires and the ice
and snow.
13. List some ways an astronaut
could keep her supplies from floating
away while orbiting around the Earth.
• Possible Answers:
– Bolt down items
– Use velcro
– Keep them tethered to the astronaut
14. As you in-line skate around the
block, what action and reaction
forces keep you moving?
• Answer: The action force is the wheels
pushing against the street or sidewalk.
The reaction force is the Earth (street or
sidewalk) pushing back on you.
15. Which of the following has the
greatest momentum? Explain.
• A charging elephant
• A jumbo jet sitting on the runway
• A baseball traveling at 100 km/h
• Answer: the elephant has much more
momentum than the baseball because
of its size. The jumbo jet has zero
momentum because it is at rest.
The Princeton Review Test
Practice (p. 97)
• 1. C
• 2. F
• 3. D