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Intro to Forces
and Motion
Ms. Graettinger
Physical Science
What is a force?
Force is a push or pull on an object or
by an object (interaction)
Balanced (no acceleration) or
unbalanced (acceleration)
A force is that which changes or tends
to change the state of rest or motion
of a body.
Examples
Magnetic (push or pull)
Elastic (push or pull)
Compression (push)
Gravity (pull)
Tension (pull)
Friction (pull)
Newton’s 3 Laws
1st : An object in motion stays in
motion. An object at rest stays at rest-until an outside force acts upon it
2nd : F=ma
3rd : For every action, there is an
equal and opposite reaction
The Force Equation
F = ma
Force = mass x acceleration
Mass is in kg
Acceleration is in m/s2
Force is in Newtons (N)
Force Equation Example
How much force is needed to
accelerate a 70-kg rider and her 200kg motorcycle at 4 m/s2?
F=ma
F=(70kg + 200kg) x (4 m/s2)
F=1080 N
Falling Objects
Any two objects falling from the
same distance, released at the
same time, will land at the same
time
Why is this?
Air Resistance
The force air exerts
on a moving object
If there is no force
except for gravity,
all objects will
accelerate at a rate
of 9.8 m/s2
Air Resistance
This force acts in the opposite
direction to that of the objects
motion
Air resistance pushes up
while gravity pulls down
Air Resistance Example
Acceleration due to Gravity on Earth
Falling objects
accelerate at 9.8m/s2
Therefore,
Weight(N)=m(kg) x a
W=m x 9.8m/s2