Name: ______________________________
Physical Science
Newton’s Laws Study Guide
Chapter 6 in book
1. What is the speed of an object?
A measure of how fast the object is moving
2. What is the velocity of an object?
A measure of how fast AND in what direction the object is moving
3. When is an object accelerating?
When the object is changing direction, speeding up, or slowing down
4. What would happen if you dropped a golf ball and a bowling ball off the top of a building?
Which would land first?
They would both hit the ground at the same time.
5. The acceleration due to gravity is the same for all objects. Explain this statement. Draw a
picture to show an example of this.
All objects accelerate (change
speed) as they move toward the
ground) at the same rate. They go
faster every second – always the
same amount of “faster”.
6. What is the rate of acceleration for all objects, due to gravitational pull? What does this
number mean?
The rate of acceleration due to gravity is 9.8 m/s/s. This means that after the
first second of falling, an object is going 9.8 meters per second. But, since it
increases by 9.8 m/s every second, after second #2, the object is falling at
19.6 meters per second. After the third second, the object is speeding
downward at 29.4 m/s.
7. If all objects fall to the earth at the same rate of acceleration due to gravity, why does a
feather drop more slowly?
Because the feather is not very dense and very flat. It has a lot of surface area.
Because of this shape, the friction from the air particles it hits on the way down
slow it down. Other examples of things that drop more slowly are flat pieces of
paper and leaves.
8. What is Newton’s First Law of Motion? Tell what it means in your own words.
“An object at rest remains at rest and an object in motion remains in motion at a
constant speed and in a straight line, unless acted on by an unbalanced force.” In
other words, if an object is still (not moving), an unbalanced force is necessary to
make it move. Once an object is moving, it will go in the same direction and at the
same speed, unless some new force stops it, slows it down, or changes its
direction.
9. The first part of Newton’s First Law talks about objects at rest remaining at rest. Are the
forces on these objects balanced or unbalanced?
Balanced; there is no motion.
10.The second part of Newton’s First Law talks about objects in motion remaining in motion
unless other forces act on it. Are moving objects experiencing balanced forces or
unbalanced forces?
Unbalanced. We know, because the objects are already moving, and unbalanced
forces produce movement.
11.What is the primary force that works against motion?
Friction is the primary force that works against motion.
12.Describe a circumstance where you want friction to work against Newton’s First Law.
(Note: I said DESCRIBE. One or two words is not a description.)
Example: If I was riding my bicycle, and there was no friction to work against
Newton’s First Law, I’d give a first push, and I would never be able to turn or
stop. The friction of my hand against the handlebars, and the tire against the
pavement, allows me to make turns – Newton’s Law wants me to go straight! The
sliding friction of the brakes allows me to stop – Newton’s Law wants me to keep
going!
13.Newton’s First Law also has another name. What is it?
The Law of Inertia. (Memory trick: “I” is the Roman numeral for one, so
remember Newton’s Law #1 is inertia, that starts with an “I” – capital “i”).
14.Copy Newton’s Second Law here:
“The acceleration of an object depends on the mass of the object, and the amount
of force applied.”
15.Now rewrite the law in your own words.
How fast something accelerates depends on two things: the mass of the object
and how much force was put on it to make it move. The less massive the object,
the faster it will tend to accelerate. Also, it a lot of force was put on it to make
it start moving, then it will tend to go faster. We know this from our real life
experiences.
16. If you pushed these two grocery carts with the same amount of force, which would
accelerate faster? Explain this using Newton’s Second Law.
The empty grocery cart will accelerate
more rapidly, because it has less mass.
Newton’s Second Law says that how
quickly something accelerates depends
on its mass, and the force put on it. If
the force is the same for both, then the
empty cart will move more quickly.
17. Yikes! Both of these vehicles are being driven carelessly, and they are about to hit that
wall!! If they are both going 20 mph, which will hit the wall with more force? Why?
The truck will hit the wall with more force. It
is more massive. Newton’s second law says
that force is equal to the mass times the
acceleration. If the acceleration is the same
for both, then the thing making the difference
is the mass.
You will use the following formulas for the next two questions:
a = F/m
F = m times a
18.If an object has a mass of 20 kg and has a force of 100 N exerted on it, what would be its
acceleration? Show your work, including which formula you used!!!
a = F/m
a = 100 N divided by 20 kg
acceleration = 5 m/s/s
19.If an object has a mass of 2.5 kg and is accelerating at 4 m/s/s, what would be the force on
the object? Show your work, including which formula you used!!!
F = m times a
F = 2.5 kg times 4 m/s/s
F = 10 N
20.Name two ways to increase the acceleration of an object.
You can increase the acceleration of an object by taking away mass (make it less
massive, like emptying a grocery cart, or a box) or by increasing the force you put
on it.
21.Copy Newton’s Third Law.
“Whenever one object exerts a force on a second object, the second object
exerts an equal and opposite force on the first.”
22.Rewrite Newton’s Third Law in your own words.
When you put a force on something there is always another force that goes with
it. That other force has the same strength (equal amount) but goes in the
opposite direction.
23.What is a “force pairs”? Give an example.
When one force is exerted, another force always happens – equal, but in the
opposite direction. So, when I sit on a chair, I exert a force on the chair, equal to
my weight, and in a downward direction. The chair is also exerting a force on me.
It pushes me up (opposite direction) and has a force that is equal to my weight
(otherwise, it would break!).
24.Explain the action of jumping on a trampoline in terms of Newton’s Third Law. Explain
what happens to you if you jump harder, using Newton’s Second Law. Draw a sketch to
help you.
Newton’s Law says when a force is applied to an object, there is an equal force
applied from the object, in the other direction. When you jump on a trampoline,
you apply force to the trampoline, and the trampoline applies a force to you.
These are the force pairs described in Newton’s Third Law. If you jump harder,
you are increasing the force, so you will accelerate more quickly, according to
Newton’s Second Law.
You apply a force to the
trampoline – a push downward.
The trampoline applies a force
to you – a push upward!
25. Using the example of the trampoline above, explain what happens to you if you jump
harder, according to Newton’s Second Law. Draw new force arrows to illustrate this.
If you jump harder, you are applying
more FORCE to the trampoline.
Newton’s 2nd law says that if you
apply more force, you will have a
greater acceleration. You will be
jumping both higher and faster.
You are jumping higher because
you hit the trampoline with a
greater force, the trampoline
will hit you back with that same
amount of force – Newton’s 3rd
law!
26.What would happen if someone who was less massive jumped on the trampoline. Would
they need to use more force, or less force, to get the same acceleration as the person in
question 31. (Hint: use the formula for Newton’s Second Law and make up some
numbers for the people’s masses to check out your prediction.)
The girl on the left has less mass
than the girl on the right.
less mass
more mass
We can use this formula to see what happens if to the acceleration if the girls apply different
amounts of force:
force = mass time acceleration
Let’s say that the girl on the left has a mass of 40kg and the girl on the right has a mass of 50
kg. We say we want them to have the same acceleration… so let’s say we want them to have an
acceleration of 2 m/s/s (every second, the girls’ speed would increase by 2 m/s).
Let’s plug in the numbers:
F = (m)(a)
F = (40 kg) (2 m/s/s)
F = 80 N
F = (m) (a)
F = (50 kg) (2 m/s/s)
F = 100 N
So, it takes MORE force for the girl with more mass to have the same
acceleration as the girl who has less mass.
27.What is momentum?
Momentum is how hard an object is to stop, once it starts moving. Momentum
depends on an object’s mass and speed. The more massive an object, the more
momentum it has. The higher the speed, the more momentum the object has.
28.When we throw a bowling ball, we can make the pins fall down (assuming we are good at
it, or the bumpers are up!). Explain what is happening, using the term momentum. Draw
a sketch to help.
When we throw the bowling ball, we cause it to move (unbalanced force). If the
bowling ball is massive, and it has a lot of speed, it can have a lot of momentum.
This means it is hard to stop. When it hits the pins, because it has so much
momentum, it knocks lots of them over. Bowling balls that are less massive don’t
have as much momentum. Also, if they are going slowly, they don’t have as much
momentum. So, the goal is to throw a heavy ball fast – and accurately, of course!
lots of momentum
means the ball is hard to stop – it
takes lots of pins to stop it!
lots of force means
the ball will go fast
29. Which has more momentum, a mouse running at 1/m north or an elephant walking at
3/m east? Explain your answer.
An elephant walking at 3/m will have more momentum, because it is more
massive and it is going faster.