Newton’s Three Laws of Motion

Isaac Newton developed three laws that help explain how forces affect motion. A force is a push or a pull. The first law describes inertia: an object tends to keep doing what it is already doing. A book resting on a desk stays put until a force moves it. A rolling skateboard keeps moving until forces such as friction or a rider’s foot slow or stop it. The second law connects force, mass, and acceleration. Acceleration means a change in speed or direction. When the same push is applied, an object with less mass accelerates more than an object with greater mass. A stronger push can also cause more acceleration. In science, this relationship is written as force = mass × acceleration. The third law says forces come in pairs. If one object pushes on another, the second object pushes back with an equal force in the opposite direction. For example, air rushing out of a balloon pushes backward, while the balloon moves forward. These laws help explain ordinary events, from a ball changing speed when kicked to a rocket moving as exhaust gases stream downward.

Check Your Understanding