Newton’s Second Law of
Motion
Mrs. Anna Ward
James Martin MS
Do Now!!!
 Draw the following in your science notebook…
 FORCE = MASS times ACCELERATION
FORCE = 1000 x .05
FORCE = 50 NEWTONS
Announcements
 Test on Newton’s Laws on Friday
 Notebook Check next Friday
Agenda
 Individual Mini Labs at our desk on Newton’s Second Law
 Guided Notes on Newton’s Second Law (F=ma)
 Partner Mini-Lab on Newton’s Third Law
 Guided Notes on Newton’s Third Law
 Video on Newton’s Laws
How are force and acceleration
related?
1. Directions: Tie a paper clip to each end of the
yarn.
2. Hold the single paper clip in the middle of your
desk; hang the other end of the yarn over the
edge. Let go and observe.
3. Add one more paper clip to the hanging end
and repeat the experiment. Observe what
happens.
4. Repeat step #3.
Questions for your notebook:
Questions:
1. What happened each time that you let
go of the yarn?
2. Explain the relationship between the
number of hanging paper clips and the
motion of the paper clip on the table.
Newton’s Second Law
Newton’s Second Law states
that the acceleration of an
object increases with increased
force and decreases with with
increased mass.
In simple terms…
 Force, mass, and acceleration have a relationship
 http://www.d123.org/olhms/ebarlos/documents/PSC0
2BAD.pdf
Newton’s 2nd law
 We describe this relationship using the formula:
F=ma
or
Force=mass x acceleration
Newton’s Second Law
 Force is measured as mass with acceleration, so…
 Kg/m/s2
 Which is also known as a NEWTON
 1 Kg/m/s2 = 1 Newton or 1 N
Newton’s 2nd Law—Apply the
Knowledge
 What force is needed to accelerate a 10 kg
shopping cart 3 m/s2?
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What do you know?
What do you want to find out?
Write the formula:
Substitute into the formula:
Calculate & Simplify:
Check that your units agree
Answer: F=30 N
CFU
 What force is needed to accelerate a 20 kg
boulder to 2 m/s2?
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What do you know?
What do you want to find out?
Write the formula:
Substitute into the formula:
Calculate & Simplify:
Check that your units agree
Answer: F=40 N
CFU
 If a force of 35N is added to a box and it
accelerates to a rate of 7 m/s2, what is the
mass of the box?
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What do you know?
What do you want to find out?
Write the formula:
Substitute into the formula:
Calculate & Simplify:
Check that your units agree
Answer: mass=5 kg
Independent Practice F=ma
1. What net force is required to accelerate a car
at a rate of 2 m/s2 if the car has a mass of
3,000 kg?
2. A 10 kg bowling ball would require what force
to accelerate down an alleyway at a rate of 3
m/s2?
3. Victor has a car that accelerates at 5 m/s2. If
the car has a mass of 1000 kg, how much
force does the car produce?
Newton’s Third Law: Investigation
1. With a partner, hook the two spring scales
together.
2. Pull gently on your spring scale while your
partner holds but does not pull on the other
side.
3. Observe and record the amount of force that
is shown on your scale and on your partner’s
scale.
4. Both of you pull together. Observe the forces
shown on each side.
Investigation Questions:
1. What happened to your partner’s force
as your force increased?
2. What happened when you both pulled?
3. Explain why you think what you observed
in each case happened.
4. Can you think of a way to use the scales
to show Newton’s first or second law?
Newton’s Third Law
Newton’s Third Law states 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.
Newton’s Third Law—in more simple
terms
Sometimes referred to as law of “EQUAL
and OPPOSITE”
For every reaction, there is an “equal and
opposite” reaction
What ever happens, there is an exact (but
opposite) force that happens as well.
CFU…
So if Nixon pushes against a
wall with a force of 25N, how
much force does the wall
exert on him, and in what
direction?
Action-Reaction Pairs
The force that is exerted on an object and
the force that exerts back are known as
action-reaction pairs.
 Example: When Abed bangs his toe into the leg of the
table, the same amount of force he exerts on the table is
exerted back on his toe.
Action-Reaction Pairs
 http://www.d123.org/olhms/dedie/d
ocuments/2-3Forces.pdf
Brainstorm…
What are some other examples
of Action/Reaction Pairs?
CFUs
What are the action reaction pairs with:
Jumping?
 Walking?
 Catching a Ball?
 Larkam’s bat hitting a baseball?
 The door shutting?
 Asia’s book bag hitting the floor?
Video…
http://www.youtube.com/wa
tch?v=2OJjbztWitk
EXIT TICKET
 Suppose Robert is holding a basketball
while standing still on a skateboard.
Justin and the skateboard have a mass
of 50kg. He throws the basketball with
a force of 10N. What is his acceleration
before and after he throws the ball?