Inertia

Beginner

The resistance of a body to changes in its motion; measured by mass.

Inertia is the tendency to resist changes in motion. Mass is its measure: the larger the mass, the larger the force needed for a given acceleration.

Worked example

A loaded truck needs a longer distance to stop than an empty one at the same speed.

Common mistake

Inertia isn't a force; it's a property.

In more detail

Inertia is the resistance of an object to changes in its state of motion, and it is measured by mass. A larger mass has more inertia.

Heavy trucks need longer distances to stop because of their greater inertia.
Washing machines spin laundry at high speed, using inertia to force water out.
It is harder to push a loaded shopping trolley than an empty one, because the larger mass resists a change in its motion.

Is inertia a force?

No. It is a property of matter describing its resistance to change in motion.

Does inertia depend on weight?

It depends on mass, not weight, so an object has the same inertia on Earth and on the Moon.

Is inertia a force?

No. Inertia is a property of mass, the resistance to a change in motion, not a force that acts on the body.