UNIT 4
MOTION & FORCES
1
Laws of Motion
2
About 300 years ago, a scientist
named Isaac Newton
had some ideas about forces and
motion
3
His ideas became known as
Newton’s Law’s of Motion
They are called laws because they
correctly explain certain happenings
around you
4
One of the Newton’s laws says that if
all the forces acting on an object are
balanced
the object will keep its state of motion
5
In other words, if the object is at rest,
or not moving
it will stay at rest, or not move
6
If the object is moving
it will keep moving
7
The state of motion will stay the same
unless the forces become unbalanced
by some other force
8
Suppose you see a soccer ball on the
grass
It is at rest
9
The force of the ground pushing up on
it is balanced
by the force of gravity pulling down on
it
10
The soccer ball will keep its state of
motion
which in this case is no motion
11
Suppose you kick the ball
You have unbalanced the forces with
the force of your kick
12
The ball will be in motion
The ball will stay in motion until some
other force comes along
13
In this case, a force called friction will
stop the ball after awhile
14
Another law of motion says that for
every action
there is an equal and opposite reaction
15
When a rocket is launched
burning fuel makes hot gases come
out of the bottom of the rocket
16
The rocket pushes on the gases and
takes off
moving away from Earth
17
The gases pushing the rocket is the
action
Action
Reaction
The rocket moving up is the reaction
18