2. Newton’s 1st Law
An object at rest or an object in motion will
stay at rest or in motion unless acted on by
an unbalanced outside force.
All objects resist motion change – inertia
The greater the mass of an object, the
more inertia it has
3. Examples
1.) You roll a bowling ball
down an alley. Its keeps on
rolling and rolling at constant
speed until it hits a pin. From
there it slows down. This is an
example of Newton’s 1st law
as it illustrates the fact that an
object in motion will stay in
constant motion unless acted
on by an outside force. In this
case, the pins were the
outside force
2.) There is a glass on a table.
It sits completely
still, undisturbed. It will
continue to be still unless
someone or something
comes by and disturbs it. This
is an example of Newton’s 1st
law because the glass would
have stayed stationery, had it
not been for an outside force.
An example of such force is
an animal knocking it over or
a person picking it up.
4. Newton’s 2nd Law
A force of an object is equal to its mass
multiplied by its acceleration.
Change in motion only occurs if a net
force is exerted on an object
The more inertia an object has, the harder
it is to accelerate
More mass is equal to less acceleration if
the acting force is the same
5. Examples
1.) Your car, which weighs
1,670 kg, is out of gas. You
start to push it at a speed of
0.05 m/s/s to the gas station.
The force you’re pushing it
with is its mass multiplied its
acceleration, according to
Newton’s law. 1,670 kg
multiplied by 0.05 m/s/s is
equal to 83.5 newtons.
Therefore, the force exerted
on your car is 83.5 newtons.
2.) You are pushing an empty
shopping cart while the
person next to you is pushing a
full one. You make eye
contact and decide to race
each other. Both of you are
exerting the same strength of
force on the carts.
However, you are going faster
than she is. This is because
Newton’s 2nd law states that
more mass is equal to less
acceleration if the acting
force is the same.
6. Newton’s 3rd Law
For every action, there is an equal and
opposite reaction.
The force exerted by the first object is
called the action force
The force exerted by the second object is
called the reaction force
7. Examples
1.) Imagine a flying bird, its
wings pushing air downward.
Since forces result from
mutual interactions, the air
must also be pushing the bird
upwards. The size of the force
on the air equals the size of
the force on the bird. The
direction of the force on the
air is opposite the direction of
the force on the bird. Action-
reaction force pairs make it
possible for birds to fly.
2.) If it were not for the
reaction force, we would be
unable to walk. As we
walk, we push onto the
ground with our feet. As we
push down, earth pushes
back up on us. This is true to
Newton’s 3rd law because the
action of placing our feet on
the ground is coupled with an
equal, opposite reaction from
earth. If the earth did not
push back, we would sink.
