Glossary · Vật lý
Inertia
An object's resistance to changes in its motion, that is, its resistance to acceleration. Mass is the measure of inertia: the more massive a body, the harder it is to change its velocity.
Newton's first law states that a body at rest remains at rest, and a body in motion remains in motion at constant velocity, unless acted on by a net external force. For that reason it is often called the law of inertia.
The common misreading: motion does NOT need a force to keep going. Force is needed only to CHANGE motion. The opposite intuition comes from friction, always present in everyday life, but not a law of motion.
Inertia does not depend on where the object is. A tonne of equipment floating on a space station is just as hard to set moving and to stop as it is on the ground, because its mass is unchanged.