Name: ______________________________
Date: ________________
Block: __________
Unit 3 Review Guide: Newton’s Laws of Motion.
NEWTON’S LAWS OF MOTION
1. State in your own words each of Newton’s Three Laws of Motion.
a. 1st Law: Objects keep their state of motion until a net force makes them do something
different.
b. 2nd Law: The Acceleration of an object depends on how hard someone pushes on it
(force) and how big it is (mass).
c. 3rd Law: Whenever something hits a second object, the second object hits the first with
the same size force but in the opposite direction.
2. What is Inertia? The tendency for an object to resist changing it motion (accelerating).
a. Which has or inertia, an elephant or a dog? How can you tell? The Elephant because it
has more mass than the dog.
3. Identify which of newton’s laws of motion describes the observations below.
a.
A swimmer pushes back on the water in order to move forwards.
Third Law
b. A space satellite flies through frictionless space even though it has no forces acting on it
to keep it moving?
First law
c. A piano starts to accelerate faster when two students push on it as opposed to just one
student.
Second Law
d. A sheet of paper is quickly pulled out from underneath a 2L bottle of soda without
spilling the soda.
First Law
4. When a hockey player runs into the side wall of the rink, they create an action force on the wall.
What is the reaction force in this scenario?
The wall pushing back on the hockey player.
a. The hockey player experiences (Less The Same More) force than the wall experiences?
Circle one.
Name: ______________________________
Date: ________________
Block: __________
5. A large engine is used to make a dump truck accelerate. If the dump truck will filled so that the
mass of the truck doubles, how would that affect how quickly the truck could accelerate?
The truck will accelerate half as much.
TYPES OF FORCES
6. Fill in the table below.
Force
Symbol for a Free Body
Diagram
Direction the Vector points on a Free Body Diagram
Weight
w
Always points straight down.
Friction
f
Always points in the opposite direction the object
is trying to move.
Normal
n
Perpendicular to the surface the object is touching
Tension
T
Whichever way the string is pulling
7. How would the weight of an object change on the moon compared to the Earth?
It would weigh less.
8. What two factors affect how strong the frictional force is between two surfaces?
How bumpy the two surfaces are and how hard they are being pressed together.
9. What does it mean to calculate the Net Force acting on an object?
To add up all the forces acting on an object and paying attention to the direction the
forces points (positive or negative.)
10. What is the Net Force acting on the box below?
3N
6N
5N
FNetx  3  6  3 N
FNet y  5
FNet  (3) 2  (5) 2
FNet  5.83 N
Fnet= ___5.83 N___
Name: ______________________________
Date: ________________
Block: __________
11. Draw a Free Body Diagram for the following situations.
A skier going down a frictionless snow covered
hill.
A ball slowing down as it rolls down the hallway.
n
n
Velocity
f
w
w
A Student using a pulley to lift a crate.
T
A student pushing a crate across a floor that is
very rough.
n
T
f
p
w
w
Practice Math Problems
12. What is the mass of a cart that accelerates at a rate of 3 m/s2 when a net force of 15 N is
acting on it?
FNet  ma
15  m(3)
m  5 kg
70 N
13. Use the diagram to the right to answer the next two questions.
a. What is the Net Force acting on the block?
Fnet y  70  30  40 N
b. If the block has a mass of 10 kg, how fast would the block accelerate?
FNet  ma
40  10a
a  4 m / s2
30 N
Name: ______________________________
Date: ________________
Block: __________
14. A string is used to hold a 2 kg bowling ball off the ground.
a. Draw a free body diagram of the forces acting on the bowling ball.
T

w
b. How much does the bowling ball weight?
w  mg
w  2(10)
w  20 N
c. If a student pulls up on the string making the bowling ball accelerate upward at 3
m/s2, how much tension will be in the rope?
FNet y  ma y
T  w  ma y
T  20  2(3)
T  26 N
15. A student is pushing a desk across the floor of the classroom. Even though there is
friction, the desk still accelerates to the right.
a. Draw a free body diagram of the forces acting on the desk.
n
f

p
w
b. If the desk has a mass of 30 kg, how much does the desk weight?
w  mg
w  30(10)
w  300 N
c. What is the Normal Force acting on the desk?
FNet y  ma y
n  w  ma y
n  300  30(0)
n  300 N
d. If the coefficient of kinetic friction between the desk and the floor is 0.3, what is
the size of the frictional force acting on the desk?
f  n
f  .3(300)
f  90 N
2
e. If the desk is accelerating at a rate of 2 m/s , how hard is the student applying a
force to the desk?
FNetx  max
p  f  ma y
p  90  30(2)
p  690 N