Force

1
Force

• Ch 5 Sec 2
• p. 115-118

2
What is force?

• A push or pull
• Scientists express force using a unit called the
  newton (N).
• -the more newtons, the greater the force.

3
A force is always exerted by one object on
another object.

• For push or pull to occur, something has to
  receive that push or pull.
• - You cant push or pull nothing!
• Examples of force
• fingers on a keyboard
• pushing a swinging door
• pulling a wagon

4
Sometimes a force does not cause motion

• You are sitting in your chair right now and
  exerting a force down on the chair, but your
  chair is not moving.
• Why?
• The Earth is also exerting a force up on the
  chair.

5
Net force

• The force that results from combining all the
  forces exerted on an object

6
Forces in the same direction--
When forces act in the same direction, they are
added together to determine the net force.
7
Forces in different directions--
When forces are in different directions, you
subtract the smaller force from the larger one to
determine the net force.
8
Unbalanced and Balanced Forces

• The net force tells you whether the forces on the
  object are balanced or unbalanced.
• Unbalanced forces produce a change in motion.
• Balanced forces produce no change in motion.

9
Unbalanced

• When the net force on an object is greater than
  zero, the forces on the object are unbalanced.
• Unbalanced forces are necessary in order to
• cause a nonmoving object to start moving
• change the motion of moving objects

10
Balanced

• When the forces applied to an object produce a
  net force of zero, the forces are balanced.
• Balanced forces will not
• cause a nonmoving object to start moving
• change the motion of moving objects

11
How can you tell if forces are balanced or
unbalanced?

• 1. Find the net force.
• - if it is zero- balanced
• - if it is greater than zero- unbalanced
• 2. Look for a change in motion.
• -no change- balanced
• -change- unbalanced

12
Homework

• Read pages 115-118
• Complete review questions 1-3 using complete
  sentences.