Transcript Newton`s Laws of Motion

Newton’s
Laws
of
Cool!
Motion
I like to sing
the abc’s!
Ouch!
What’s with the apple
dude?
INERTIA
Tendency of objects to
resist changes in motion
Larger mass = more
resistance to change
First Law of
Motion: the
Law of Inertia
In his own words:
An object at rest will
remain at rest and an
object in motion will
remain in motion at
constant velocity
unless acted upon
by an unbalanced force.
Second Law of
Motion:
The law of
Acceleration
2nd Law of Motion
Force = Mass x Acceleration
F = m x a or a = F/m
An unbalanced force will
cause an object to accelerate
Acceleration is related to the
amount of force and mass
vs.
Third Law of
Motion:
The law of
Interaction
rd
3
Law of Motion
For every action force ,
there is an equal and
opposite reaction force
-Forces occur in equal
and opposite pairs
The following slides are
examples of the laws
Sled dogs join together to exert
a force to overcome the inertia
of the sled.
What will cause the sled to stop?
NEWTON'S FIRST LAW
When the car hits the cement road divider it is stopped (an outside force stops it from moving). The
crash dummy, however, is not so lucky. Since he is not wearing a seat belt, and is not connected to
the car, he will continue to move at 60 mph. This means he will go flying out through the front
windshield (don't try this at home).
The dummy will fly through the air until he hits the ground. This is because the earth's gravity stopped him
from moving any further (his trajectory is a combination of the downward force of gravity, and the
horizontal force of the moving car). If this collision had happened in zero-g, in a vacuum, the dummy
theoretically would keep on hurtling away from the car at 60 mph
Why must he
exert more
energy to start
running from a
stopped
position than
to continue
running once
he has begun?
BOB's van, which weighs 2,000 kg, is out of gas. BOB is trying to
push the car to a gas station, and he makes the car go 0.05 m/s/s.
Using Newton's 2nd Law, you can compute how much force BOB
is applying to the car.
Although the
ball has
small mass,
its
acceleration
off the
racket is
great. Why?
Unit of Force
Mass
kilograms
Acceleration m/sec/sec
force
newtons(N)
1N = 1 kg x 1 m/sec/sec
Why do huge trucks need to exert
great force to accelerate than small
vehicles?
How much force is
needed to accelerate a
1400 kg car 2 m/sec/sec?
Step 1:
F = MA
Step 2: F = 1400 kg x 2 m/sec/sec
Step 3: F = 2800 kg-m/sec/sec
or 2800 N
How much force
is needed
to
accelerate a 66-kg
skier 1m/sec/sec?
F= 66 newtons
What is the force on
a 1000-kg elevator
that is falling freely
at 9.8 m/sec/sec?
F= 9800 newtons
Here we see BOB punching
Mike in the face.
Here we see Space Man Spiff's rocket ship.
BOB (who isn't very bright) is tired of pushing his van to the gas
station. He gets an idea -- "Hey! I go much faster when I am rollerblading than when I am walking. Why don't I wear my rollerblades!" So BOB gets his roller blades from the back of his van,
and starts pushing.
Since every action has an equal and opposite reaction,
when BOB pushes the van, the van pushes BOB. BOB
weighs 50 kg, and the van weighs 2,000 kg. Thanks to
the Second Law, you can compute how much BOB and
the van will move after 1 second (hint: use A=f/m).
Ooops…What happened here?
How does
the third
law
of
motion
explain the
movement
of a water
sprinkler?