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Newton’s Laws Notes
Newton’s 1st Law is the Law of
“An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same
speed and in the same direction unless acted upon by an external force.”
Why does Newton think you should always wear your seatbelt?
Inertia is the tendency of an object to resist changes in its
or to resist
.
More mass = more inertia
Newton’s 2nd Law
Pertains to the behavior of objects for which all existing forces are
balanced.
The second law states that the acceleration of an object is dependent upon two variables
the
acting upon the object
and the
of the object.
Summed up in this equation:
How else can this equation be written?
The acceleration of an object depends
the object, and
upon the net force acting upon
upon the mass of the object.
As the force acting upon an object is increased, what must happen to the acceleration?
As the mass of an object is increased, what must happen to the acceleration of the object?
Solve for the unknown value:
Newton’s 3rd Law
For every action, there is an
and
reaction.
Forces always come in pairs - equal and opposite action-reaction force pairs
While driving down the road, a firefly strikes the windshield of a car and makes a quite obvious mess in
front of the face of the driver. The firefly hit the car and the car hits the firefly.
Which of the two forces is greater: the force on the firefly or the force on the car?
For years, space travel was believed to be impossible because there was nothing which rockets could
push off of in space in order to provide the propulsion necessary to accelerate. This inability of a rocket
to provide propulsion is because ...
a. ... space is void of air so the rockets have nothing to push off of.
b. ... gravity is absent in space.
c. ... space is void of air and so there is no air resistance in space.
d. ... nonsense! Rockets do accelerate in space and have been able to do so for a long time.
A gunpowder explosion creates hot gases which expand outward allowing the gun to push forward on
the bullet. Consistent with Newton's third law of motion, the bullet pushes backwards upon the gun.
The acceleration of the recoiling rifle is ...
a. greater than the acceleration of the bullet.
b. smaller than the acceleration of the bullet.
c. the same size as the acceleration of the bullet.
If the action force is opposite and equal why do they not cancel? Action and Reaction forces do not
cancel because they are acting on
objects!
Action force:
Baseball pushes glove leftwards.
Bowling ball pushes pin leftwards
Enclosed air particles push balloon wall outwards
Review:
Newton’s First law:
Newton’s Second law:
Newton’s Third Law:
Reaction force: