What are examples of inertia of motion?

Inertia of motion means a moving body keeps moving at the same speed and direction unless a force acts; examples include passengers lurching forward in a suddenly stopping bus and a ball rolling on a smooth surface continuing to roll.

Inertia of motion is a part of Newton’s first law. A moving object resists change in its state of motion. Without an external force like friction or a push, it will keep its velocity.

Common examples

• Bus stop jerk: When a bus brakes, your body tends to keep moving forward.
• Tablecloth trick: With a quick pull, dishes tend to stay at rest relative to the table because their motion is unchanged for a brief instant.
• Rolling ball: On very smooth ice, a puck keeps gliding far because little friction acts.
• Seat belts: Belts stop your forward motion during a sudden stop.
• Stone from a sling: The stone moves in the tangential direction when released, keeping its motion.
• Train example: Inside a steadily moving train, dropped objects fall straight down relative to you because they keep the train’s horizontal motion.