# What is a Force? ```Section 2
Chapter 16
Matter in Motion
 This section defines force and gives
examples of different kinds of
forces.
 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


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object.
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
(acceleration).
 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.
```