Name: ______Score: _____/30
Self Assessment: Newton’s Laws of Motion
1. Define unbalanced forces. How can you tell by looking at an object if the forces on
it are unbalanced?
True or False. Explain.
2. ______When forces are balanced something does not move.
3. ______When forces are balanced something moves at a constant speed.
4. ______When forces are balanced something accelerates.
5. ______When forces are unbalanced something does not move.
6. ______When forces are unbalanced something moves at a constant speed.
7. ______When forces are unbalanced something accelerates.
8. What is friction?
9. – 11. Name/Describe the three kinds of friction
12. – 13. Name two ways to increase friction and two ways to decrease friction
14. Explain what inertia is and what other property of matter it depends on.
Use the formula F=ma to solve the following. Show your work! Don’t forget the correct
units and sig figs.
15. ______What is the acceleration of a truck with a mass of 1200 kg
moving because of a 7800 N force?
16. ______What is the mass of a soccer ball that is accelerating at
11.5 m/s/s because of an applied force of 167 N?
17. ______How much force does a 40.3 kg object exert if it’s moving at
20. m/s2?
18. Earth is pulling me down. We call that gravity. If gravity is the action force, what
is the equal and opposite reaction force?
Identify which Law of Motion each is by placing a 1, 2 or 3 in the blank
19. ______You’re in a car that slams on the brakes and you go flying forward
20. ______When you hit a nail with a hammer, they both feel the same force
21. ______The nail in #2 moves more than the hammer does.
22. ______I can throw a baseball farther than a shotput.
23. ______When I throw the baseball, it would go straight, if it weren’t for gravity
and air resistance.
24. ______It takes more effort to push a full shopping cart than an empty one.
25. ______The weight of an object is its mass times the acceleration due to gravity.
26. ______I hit a ball with a bat. The same force is exerted on both objects.
27. ______I spin a yoyo in a circle. If I let go of the string, it flies off in a straight line.
Two people of different mass are on ice skates as shown. When
they push off, describe what happens
28. Using Newton’s 1st Law of Motion.
29. Using Newton’s 2nd Law of Motion.
30. Using Newton’s 3rd Law of Motion.
Name: __Answer key__ Score: _30_/30
Self Assessment: Newton’s Laws of Motion
1. Define unbalanced forces. How can you tell by looking at an object if the forces on
it are unbalanced?
Total forces are not equal; net force not = 0
The object accelerates (changes speed,
direction or both)
True or False. Explain.
2. __True*___ When forces are balanced something does not move.
* kinda. It can be not moving. But it is also
true that it can move with a constant speed.
A better way to put this is to say that when
forces are balanced something is not changing its motion. That is certainly true.
3. __True___ When forces are balanced something moves at a constant speed.
If the forces are balanced there is no change
in motion, so it keeps doing whatever it was doing.
4. __False___ When forces are balanced something accelerates.
It takes unbalanced forces to change motion
(accelerate) see Newton’s First Law of Motion.
5. __False___ When forces are unbalanced something does not move.
According to Newton’s First Law of Motion,
unbalanced forces lead to acceleration … motion.
6. __False___ When forces are unbalanced something moves at a constant speed.
According to Newton’s First Law of Motion,
unbalanced forces lead to acceleration (change in speed or direction or both).
7. __True___ When forces are unbalanced something accelerates.
Newton’s First Law of Motion says so.
8. What is friction?
A force that resists/opposes (acts opposite to)
motion.
9. – 11. Name/Describe the three kinds of friction
Static: when objects are at rest/not in motion
Kinetic (sliding): when objects are flat and
moving (sliding)
Kinetic (rolling): when objects rounded and
moving
12. – 13. Name two ways to increase friction and two ways to decrease friction
Increase: press together more/add more force,
roughen up the surface
Decrease: smooth the surface, add lubricants
(wax, oil), streamline (really just smoothes
the surface for air molecules)
14. Explain what inertia is and what other property of matter it depends on.
Tendency of an object to resist changes in
motion
Depends on mass. More mass = more inertia
Use the formula F=ma to solve the following. Show your work! Don’t forget the correct
units and sig figs.
15. _6.5 m/s2_ What is the acceleration of a truck with a mass of 1200 kg
moving because of a 7800 N force?
F = ma 7800 = 1200 (a) (div. both sides by 1200)
a = 7800/1200
a = 6.5 (2 sig figs)
16. _14.5 kg _ What is the mass of a soccer ball that is accelerating at
11.5 m/s/s because of an applied force of 167 N?
F = ma 167 = (m) 11.5 (div. both sides by 11.5)
m = 167/11.5
m = 14.521739813 (3 sig figs)
17. __810 N__ How much force does a 40.3 kg object exert if it’s moving at
20. m/s2?
F = ma F = 40.3 (20.) 806 (2 sf)
18. Earth is pulling me down. We call that gravity. If gravity is the action, what is the
equal and opposite reaction?
You are pulling back on the Earth! (Why doesn’t the Earth move then? Well, technically it does, but not a whole lot because it has more inertia)
Identify which Law of Motion each is by placing a 1, 2 or 3 in the blank
19. ___1___ You’re in a car that slams on the brakes and you go flying forward
20. ___3___ When you hit a nail with a hammer, they both feel the same force
21. ___2___ The nail in #2 moves more than the hammer does.
22. ___2___ I can throw a baseball farther than a shotput.
23. ___1__ When I throw the baseball, it would go straight, if it weren’t for gravity
and air resistance.
24. ___2___ It takes more effort to push a full shopping cart than an empty one.
25. ___2___ The weight of an object is its mass times the acceleration due to gravity.
26. ___3___ I hit a ball with a bat. The same force is exerted on both objects.
27. __1__ I spin a yoyo in a circle. If I let go of the string, it flies off in a straight line.
Two people of different mass are on ice skates as shown. When
they push off, describe what happens
28. Using Newton’s 1st Law of Motion.
The more massive person has more inertia and will move more slowly. Once they move they are both objects in motion and will stay that way in a straight line and at the same velocity until an unbalanced force (friction) changes that.
29. Using Newton’s 2nd Law of Motion.
They have the same force between them, so the more massive person will accelerate less, and the less massive one will accelerate more.
30. Using Newton’s 3rd Law of Motion.
The action force is them pushing against each other, the equal and opposite reaction force is the other person pushing back. That’s why they move backwards.
Note: it’s the forces that are equal and opposite, but Newton I & II describe how the motion is not equal (because of mass and inertia)!