What is a Force?

Section 2
Chapter 16
Matter in Motion
 This section defines force and gives
examples of different kinds of
 We will learn to determine the net
force on an object and to compare
balanced and unbalanced forces.
 In science , a force is simply a push or pull.
 All forces have both size and direction.
 Forces are everywhere, anytime you see an
object in motion, you can be sure that its
motion was created by force.
 Scientists express force using a unit called
the newton (N). The more newtons, the
greater the force.
 All forces are exerted by one object on another
For any push to occur, something has to receive the
push. The same is true for any pull.
It is not always easy to tell what is exerting a force
or what is receiving a force.
You cannot see what exerts the force that pulls
magnets to refrigerators.
The air you breathe is an unseen receiver of a force
called gravity.
 Often more than one force is exerted on an
object at the same time.
 The net force is the force that results from
combining all the forces exerted on an object.
 To calculate net force when the forces are in the
same direction, you just the forces together.
 When forces are in different directions, you
subtract the smaller force from the larger force.
 When a net force on an object is not zero, the forces on
the object are unbalanced.
 Unbalanced forces produce a change in motion
 Unbalanced forces are necessary to cause a nonmoving
object to start moving. They also are necessary to
change the motion of moving objects.
 An object can continue to move even when the
unbalanced forces are removed.
 When the forces applied to an object produce a net
force of zero, the forces are balanced.
 Balanced forces do not cause a nonmoving object to
start moving, nor will it cause a change in the motion
of a moving object.
 Many objects around you have only balanced forces
acting on them.