Newton’s Laws of Motion Reading Guide
CLASS COPY! Answer questions in COMPLETE SENTENCES in your Science Notebook.
Write down the section headings before answering the questions that follow.
2.1: Forces Change Motion
1. What are the three types of forces? Define and write an example for each one.
1) Contact Force: when one object pushes or pulls another object by touching it; possible examples: the force
your shoe & the ground exert on each other when you walk, turning a page in a book, pushing a broom, etc.
2) Gravity: the force of attraction between two masses; possible examples: Earth’s gravity on you, gravity
between the earth and the moon, dropping a coin, etc.
3) Friction: a force that resists motion between two surfaces that are pressed together; possible examples:
skate wheels on a road, sliding across tile, etc. (any situation where two surfaces are in contact and one is
trying to slow the other down)
2. What makes force a vector? It has both size and direction.
3. What is a net force? The overall force acting on an object when all of the forces acting on it are combined.
4. Make sketches for the following concepts. Use arrows to represent forces.
Concept
Example Sketches
Balanced & Unbalanced
Forces
Forces on Moving Objects
5. Why did Galileo use a thought experiment instead of working with real objects? A world without friction could
exist only in thought.
6. What does Newton’s first law state? That objects at rest remain at rest and objects in motion remain in motion
with the same velocity, unless acted upon by an unbalanced force.
7. How does Newton’s first law tell what will happen to the baseball when hit by the bat? The baseball is acted
upon by an unbalanced force (the bat). This causes the motion of the ball to change direction.
8. What is inertia? An object’s resistance to having its state of motion changed
9. How is the inertia of an object related to its mass? The greater its mass, the greater its inertia
2.2: Force and Mass Determine Acceleration
10. What three concepts are involved in Newton’s second law? Force, mass, & acceleration
11. What does Newton’s second law state? The acceleration of an object increases with increased force and
decreases with increased mass; the direction in which an object accelerates is the same as the direction of the
force.
12. What is the standard unit of force and what is the equation used to calculate force? Newton (N); Force = mass ×
acceleration (F=ma)
13. Copy down an example of a force problem.
14. If the same force is applied to two objects of different mass, which object will have the greater acceleration?
The object with less mass
15. Explain how a rocket continues to accelerate after launch. If the force remains the same, and an object loses
mass, it will speed up. As a rocket uses up its fuel, it becomes lighter. The force stays the same, so the rocket
speeds up.
16. How does Newton’s second law apply to changing the direction of an object? Newton’s second law says that if
you apply a force to an object, it will accelerate in the direction of the force.
17. What force keeps an object moving in a circle? In what direction does this force act? Centripetal force. Toward
the center of the circle.
18. If you were to whirl a ball on a string, in what direction would the centripetal force be pointing? The force is
always pointing along the string toward your hand.
19. If an object in circular motion begins to move faster, what happens to the centripetal force? It increases
2.3: Forces Act In Pairs
20. What does Newton’s third law state? That every time one object exerts a force on another object, the second
object exerts a force that is equal in size and opposite in direction back on the first object.
21. What moves a jellyfish through water? As the jellyfish applies a downward force on the water, the water applies
an equal force on the jellyfish.
22. What is an action/reaction force pair? The force that is exerted on an object and the force that the object exerts
back
23. Identify the action/reaction forces in the three bulleted examples on page 58. 1) the rocket’s engine pushed
exhaust downward and the exhaust pushed back on the rocket; 2) force of toe on table and force of table on
toe; 3) force of hand on table and force of table on hand.
24. What is the difference between action and reaction forces and balanced forces? While balanced forces act upon
a single object, action and reaction forces act on different objects.
25. Explain how the three laws describe motion. Every object in motion would remain in motion if another force,
such as friction, did not stop it. The acceleration of an object depends on force and mass. Every object in motion
must exert an equal but opposite force on the object that pushed it.
26. You are standing on a skateboard not moving anywhere. You want to move but are too lazy to push with your
feet. Using Newton’s third law, explain how you could move. Throw an object in the opposite direction you
want to move.
2.4: Forces Transfer Momentum
27. What is momentum? A measure of mass in motion. The momentum of an object is the product of its mass and
velocity.
28. What determines the momentum of an object? The objects mass and velocity.
29. What is the standard unit of momentum and what is the equation used to calculate momentum? Kilogrammeter per second (Kg●m/s); momentum = mass × velocity (p=mv)
30. Copy down an example of a momentum problem.
31. Compare and contrast momentum and inertia. Both depend on mass, but momentum depends on velocity,
while inertia does not.
32. When two objects collide, what do they exchange? Energy and momentum
33. If a bowling ball and a tennis ball collide, which ball will have the greater change in velocity? The tennis ball
34. How does friction affect the collision of two objects? Friction acts as an outside force to slow an object(s)
velocity; it reduces the amount of momentum in the object(s).
35. What is meant by ‘conservation of momentum’? Give an example. The amount of momentum a system of
objects has does not change as long as there are no outside forces acting on the system. Possible examples:
when a bat hits a ball, when two cars collide
36. How are some types of collisions different from others? In some collisions, the objects separate and travel
separately. In others, the objects stick together and travel with their combined momentum.
37. How is conservation of momentum related to Newton’s third law? Conservation of momentum is another way
of looking at Newton’s third law. Newton’s third law describes how for every force there is an equal and
opposite force, and conservation of momentum works because of this principle.
38. Under what condition is momentum not conserved? Moment is not conserved if outside forces act on the
system