1. Chapter 5 Matter In Motion
Section 2 – What Is A Force? pp

2. FORCES Where do you see a force happening in the room right now?
Which object is exerting the force? Which object us receiving the force?

3. IMPORTANT DEFINITIONS
Force – a push or a pull
All forces have both a size (a number) and a direction

4. FORCES
When forces are in the same direction, add the forces together to determine the net force (in the same way you added together the velocities of objects that were traveling in the same direction to get the resultant velocity.)
See Figure 3 on p. 125 of your text.

5. Calculating Net Force
When the forces are in different directions, subtract the smaller force from the larger force (in the same way that you subtracted the smaller velocity from the larger velocity when they were in different directions to get the resultant velocity.)
See Figure 4 on p. 126 of your text.

6. Units used to Measure Force
Newton (N) – the SI unit of force
Named for Sir Isaac Newton
Weight is a force. Force can also be measured in pounds and tons.

7. BALANCED AND UNBALANCED FORCES
When the net force in an object is not zero, the forces on the object are unbalanced.

8. UNBALANCED FORCES
Unbalanced forces produce a change in motion (acceleration)
Unbalanced forces are needed to cause a nonmoving object to begin to move
Unbalanced forces are also needed to change the motion of moving objects.

9. BALANCED FORCES
When the net force on an object is zero, the forces are balanced.
Balanced forces do not cause a nonmoving object to begin moving.
Balanced forces will not cause a change in motion of a moving object.