Transcript Newton’s Laws of Motion - Montville Township School District

Newton’s
Laws of
Motion
I. Law of Inertia
II. F=ma
III. Action-Reaction
1st Law of Motion
(Law of Inertia)
An object at rest will stay at
rest, and an object in motion
will stay in motion at
constant velocity, unless acted
upon by an unbalanced force.
Newton’s First Law
(law of inertia)
INERTIA is a property of an object
that describes how much it will resist
change to the motion
 more
____ means more ____

mass
inertia
Newtons’s 1st Law and You
Don’t let this be you. Wear seat belts.
Because of inertia, objects (including you) resist changes
in their motion. When the car going 80 km/hour is stopped
by the brick wall, your body keeps moving at 80 m/hour.
If objects in motion tend to stay in
motion, why don’t moving objects keep
moving forever?
Things don’t keep moving forever because
there’s almost always an unbalanced force
acting upon them.
A book sliding across a table slows
down and stops because of the force
of friction.
If you throw a ball upwards it will
eventually slow down and fall
because of the force of gravity.
1st Law

Unless acted
upon by an
unbalanced
force, this golf
ball would sit on
the tee forever.
1st Law

Once airborne,
unless acted on
by an
unbalanced force
(gravity and air
– fluid friction),
it would never
stop!
2nd Law
NEWTON’S SECOND LAW OF
MOTION



The acceleration of an object depends on
the mass of the object and the amount of
force applied to it.
Equation: F = m∙a
Force = mass times acceleration
NEWTON’S SECOND LAW OF
MOTION

In other words…
 Force causes an object to accelerate,
while the object’s mass resists the
acceleration.
 The larger the object (the more mass it
has), the harder it is to accelerate.
Check Your Understanding

1. What acceleration will result when a 12 N net force applied
to a 3 kg object?
12 N = 3 kg x 4 m/s/s

2. A net force of 16 N causes a mass to accelerate at a rate of 5
m/s2. Determine the mass.
16 N = 3.2 kg x 5 m/s/s

3. How much force is needed to accelerate a 66 kg skier 1
m/sec/sec?
66 kg-m/sec/sec or 66 N
NEWTON’S THIRD LAW OF
MOTION



In other words…
For every action there is an equal and
opposite reaction.
ACTION-REACTION FORCE PAIRS DO NOT
ACT ON THE SAME OBJECT! See Figure 7 &
Figure 8 on p. 164.
Other examples of Newton’s
Third Law

The baseball forces the
bat to the left (an
action); the bat forces
the ball to the right (the
reaction).
Reaction: road pushes on tire
Action: tire pushes on road
1stlaw: Homer is large and has much
mass, therefore he has much inertia.
Friction and gravity oppose his motion.
2nd law: Homer’s mass x 9.8 m/s/s
equals his weight, which is a force.
3rd law: Homer pushes against the
ground and it pushes back.