Physics II Day 13: Calculating Force (f=ma)
Newton’s second law can be expressed as force = mass times acceleration!
Why?
·
If you increase the mass, then it requires more
force.
·
If you want the object to go faster, it requires
more force!
So now we can calculate_______________ force in Newtons using force = mass times
acceleration.
Putting it together…
So if more mass means it is harder to accelerate an
object, how could we find out how much an object is going to accelerate? Take
force and divide_______________
it by mass.
Physicists use something called variable__________ to represent
what they know or don’t know in an equation.
Variables are usually symbolized by the first letter of
what is being measured:
Force = f
Mass = m
Acceleration = a
So to calculate force or acceleration, you must:
·
Identify what you knowP____________
·
Identify what you don’t know________
·
If your unknown is acceleration, you use
acceleration = force divided by mass
·
If your unknown is force, you use force = mass
times acceleration
· Formulas: force = mass x acceleration;
acceleration = force ÷ mass
Let’s Try as a Class
1.
Kenneth
needs to accelerate a box 2 m/s^{2}. The box weighs 8 kilograms. How
much force will he need to accelerate it?
2.
What
if the box weighed 10 kilograms?
3.
What
if the box only weighed 4 kilograms, but he wanted to accelerate it 4 m/s^{2}?
With a Shoulder Buddy:
1.
Juan pushes his brother into a swimming pool
with a force of 65 newtons. If his brother weighs 41 kilograms, at what rate
will he accelerate?
Known:

Formula:

Unknown:

Solve:

2.
Which object will require more force to
accelerate?
a)
2 kg book b)
4 kg box c) 10 kg crate d) 15 kg shelf
3.
You are trying to design a scooter that
accelerates at a rate of 12 m/s^{2}.
If the scooter weighs 22 kilograms, how much force will have to be exerted on the scooter?
Known:

Formula:

Unknown:

Solve:

4.
With the pulley, a force of 81 newtons is being
exerted on the 4 kg weight. At what rate will the weight accelerate?
Known:

Formula:

Unknown:

Solve:

Now You Try On Your Own
1) A 3kilogram
pipe is falling at a rate of 10 m/s^{2}. With how much force is gravity pulling on the pipe?
Known:

Formula:

Unknown:

Solve:

2) 3) Ms. Trevino is
moving the desks in her room. If she pushes on a desk with a force of 25
newtons, how much will it accelerate
if it weighs 4 kilograms?
Known:

Formula:

Unknown:

Solve:

3) In order to knock down all the pins, a bowling ball
must be accelerating at a rate of 1.8 m/s^{2}. If the bowling ball
weighs 9 kilograms, with what force
will you have to roll it?
Known:

Formula:

Unknown:

Solve:

4) You have been
designing a scooter and are unhappy with how quickly it accelerates. If you
can’t change the motor of the scooter and make it exert more force, what can
you do to make the scooter accelerate more?
a)
Decrease
the mass of the scooter
b)
Increase
the mass of the scooter
c)
Give the
scooter bigger wheels
d)
In this situation,
there is no way to make the scooter accelerate faster.
5) Which of the
following describes why big trucks usually use more gas than small cars?
a)
Big trucks
have more inertia
b)
Since they
are larger, trucks require more force to accelerate
c)
There is
more friction between a big truck and the road
d)
All of the
above
e)
None of
the above
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