What is the definition of inertia. explain in layperson terminology what this means?

Question

what's layperson terminology?

Answer 1

Superb question.

Inertia is mass.

Mass is just how much stuff there is in a thing.

For instance a boulder has more stuff in it than a pebble.

And even in outer space it would be harder to make a big boulder move faster than a pebble.

No one knows what causes matter (stuff) to have inertia.

Some scientists consider it to be one of the fundamental questions of the universe.

Answer 2

Inertia is the amount of resistance an object has to changes in it's motion.  Inertia is related to mass.  The more mass an object has, the more inertia it has.  An elephant is harder to move than a mouse (even in space) because it has more mass and therefore more inertia.

It's not entirely true that we don't know what causes things to have mass.  The higgs-boson is the theoretical particle that gives matter it's mass.  It's the only particle predicted by the standard model that has not yet been observed.  We're hoping to observe it when the Large Hadron Collider comes online later this year.