Sec:3 Motion and Forces

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

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

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

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

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

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