Force and Motion
Physical Science
Forces and Motion

Forces can create
changes in motion
(acceleration or
deceleration).
Motion can be described
as:
A
change in an
object’s position.
Definition of a Force
A
force can be defined as any
push or pull exerted on a body.
 The
.
unit of force is the Newton
Balanced Force

A force that
produces no
change in an
object’s motion
because it is
balanced by an
equal yet
opposite force.
No
change in
motion
Balanced Forces
Unbalanced Forces
Are forces that
result in an
object’s
motion being
changed.
+
Unequal forces pushing in opposite
directions that cause a change in
motion.
The object will do one of the following:
>Speed Up
>Slow Down
>Change the Direction of its Motion
In other words….
The Body will Accelerate
Friction
A force that opposes, or works
against, motion of two objects that
are touching.
Friction
•
•
Friction causes an
object to slow down
and stop.
Since the amount of
energy stays constant,
the energy becomes
heat.
Universal Law of Gravity
All objects in
the universe
attract each
other by the
force of
gravity.
Universal Law of
Gravity
Gravity varies depending
on two factors:
1) the mass of the object
doing the pulling, and
2) the distance from the center
of that object
On Earth gravity = 9.8 m/s/s
For
every
second that an
object falls its
speed increases
by 9.8 m/s
Why is the mass the same but the weight
different?
Weight is measured in Newton
The resultant force

When two or more forces are acting
on a body, their combined effect can
be represented by one force which is
referred to as the ‘resultant force’.
(a) Resolving two forces which act in the same
straight line

If both forces act in the same straight
line and in the same direction the
resultant is their sum,
if the forces act in opposite directions the
resultant is the difference of the two
forces and acts in the direction of the
larger of the two forces.
Practice! Find the resultant
force of the following:
20 N
15 N
15 N
25 N