1. Sec:3 Motion and Forces

2. Force Force- is a push or pull that one body exerts to another
Ex: Passing a basketball or kicking a soccer ball
Sometimes it is obvious that a force is being applied, but some forces aren’t so noticeable. Ex: Force of the floor against your feet

3. Changing motion A force can cause the motion of an object to change
Ex: Hitting a tennis ball with a racket. As the racket strikes the tennis ball with a force that causes the ball to stop and move the opposite direction
The velocity of the tennis ball changed

4. Balanced forces Force does not always change velocity
When two or more forces act on an object at the same time, the forces combine to form the net force
Forces on an object that are equal in size and opposite direction are called balanced forces. Ex: Fig.16A

5. Unbalanced forces
When unequal forces are pushing in opposite directions, a net force occurs in the direction of the larger force
Ex: Fig16B
When forces push in the same direction, the forces are combined or added together
Ex: Fig16C

6. Inertia
Inertia is the tendency of an object to resist any change on its motion. Ex: Fig.17
Velocity of an object remains constant unless a force changes it
The inertia of an object is related to its mass. The greater the mass of an object is, the greater the inertia. Ex: Bowling ball verses a tennis ball

7. Newton’s 1st law of Motion
Law of inertia: An object moving at a constant velocity keeps moving at that velocity unless a net force acts on it
Ex: Fig.18