NEWTON’S LAWS
Newton’s 1st Law of Motion
Object in motion stays in
motion
And Objects at rest stay
at rest
Until they are acted upon by unbalanced forces.
Law of Inertia is another name
for Newton’s 1st Law
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Tendency for an object to stay
at rest or moving in a straight
line at a constant speed.
The mass (m measured in kg)
of an object determines its
inertia
Unit of Force
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Unit of mass is kg

Unit of Acceleration is m/s/s
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1 kg · 1 m/s/s = 1 kg · m/s/s = 1
Newton (N)
Resulting in Force unit called a
Newton (N)
Newton’s 2nd Law or
the Law of Acceleration
Force = Mass· Acceleration
F = ma
Weight (pull of gravity) is a commonly measured force,
calculated by F=mg, g is the acceleration due to gravity
9.8 m/s2
Newton’s 2nd Law of Motion
The greater the mass
of an object, the
greater the force
required to change
its motion.
Newton’s 2nd Law of Motion
The greater the acceleration
of an object, the greater the
force required to change its
motion.
Your Turn!
How much force is needed to
accelerate a 1,300 kg car at a rate
of 1.5 m/s2?
To solve this:
F=ma
or
= 1300Kg x 1.5m/s2
F = 1950 N
Newton’s 3rd Law of Motion
Forces always work in
pairs
For every action force
there is an equal and
opposite reaction force.
Newton’s 3rd Law of Motion
All forces come in actionreaction pairs
Ex: feet push backward
on floor, the floor
pushes forward on feet
Newton’s 3rd Law of Motion
Rocket and Jets-
walls
of the fuel compartment
push backward on igniting
gases, gases push forward
on the fuel compartment
(and the rocket) so it
rises.
Newton’s 3rd Law of Motion
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Rowing a boat
Name the Action
Reaction pair of
forces?
Action: Oar pushes water back.
Reaction: water pushes boat forward.
Friction
A force that acts in a direction opposite to the
motion of two surfaces in contact with each
other.