Chapter 5 Matter In Motion Section 2 – What Is A Force? pp. 124 - 127

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?

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

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.

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.

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.

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

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.

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.