ABSTRACT
Central to the laws of mechanics is the concept of force. Our idea of force is closely related to muscular activity. When we push or pull on an object, we exert a force on it (Figure 3.1). When we push a lawn mower across a yard, pull a hand truck loaded with boxes, push against the arms of a chair to get up from it, or when we turn the ignition key with our index nger and thumb to get the car started, we are applying a force. These forces associated with muscular activity are not the only ones that exist in nature. When you bring a small magnet near a nail, a magnetic force pulls the nail toward the magnet; and a gravitational force keeps the moon orbiting around the earth and the earth around the sun, and keeps us attached to the ground.
