The Principle of Inertia

The Principle of Inertia states that an object will remain at rest or move at a constant speed in a straight line unless acted upon by an external force. Essentially, objects tend to keep doing what they’re already doing unless something causes a change. For example, a stationary car stays still until a force (like your foot on the brake) makes it move, and a rolling ball keeps moving until friction or another force slows it down. This principle explains the natural resistance objects have to changing their current state of motion.