Newton's Laws of Motion

NEWTON’S
LAWS

, © T COLLINS 2025


NEWTON’S LAWS OF MOTION

DEFINITIONS:

Newton's 1st law of motion: A body will remain in its state of rest or motion at
constant velocity unless a non-zero resultant/net
force acts on it.

Inertia: the resistance of an object to any change in its state
of motion.

Newton's 2nd law of motion: When a resultant/net force acts on an object, the
object will accelerate in the direction of the force at
an acceleration directly proportional to the force
and inversely proportional to the mass of the object.

Newton's 3rd law of motion: When object A exerts a force on object B, object B
SIMULTANEOUSLY exerts an oppositely directed
force of equal magnitude on object A.




CALCULATING Fnet:

ALWAYS draw your vectors head to tail first so that you have an idea of which way the
resultant (net) force should act. This is a good way to double check your final answer.

Choose a positive direction. If you always use right as + and up as + you’re less likely to
get confused. In that case:



1D Fnet = right – left OR Fnet = up – down
problems:
2D ® Calculate the net horizontal and net
problems: vertical like a 1D problem.
® Draw the components head-to-tail.
® Pythag (magnitude) and trig (direction).




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