Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

What is inertia?

ScienceLesson on requestFree to read

Quick answer

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.

Key things to understand

  1. It's resistance to changes in motion.
  2. Objects at rest stay at rest; moving objects keep moving.
  3. More mass means more inertia.
  4. It's the basis of Newton's first law of motion.

People also ask

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.

Part of the guide: Cars, Trains, Planes & Ships →