Science
What is Inertia?
Inertia is an object's resistance to changes in its motion. A still object stays still, and a moving object keeps moving, unless a force acts on it. It's the heart of Newton's first law — and why you lurch forward when a car suddenly brakes.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains inertia.
Key things to understand
- 1It's resistance to changes in motion.
- 2Objects at rest stay at rest; moving objects keep moving.
- 3More mass means more inertia.
- 4It's the basis of Newton's first law of motion.
Frequently asked questions
- What is inertia?
- The tendency of an object to resist changes to its state of motion unless acted on by a force.
- What's an everyday example of inertia?
- You lurch forward when a car brakes suddenly, because your body keeps moving.
- How are inertia and mass related?
- The more mass an object has, the more inertia it has, so the harder it is to start or stop.