Inertia

[Sarah]

That property of matter by which it tends when at rest toremain so, and when in motion to continue in motion, and in the samestraight line or direction, unless acted on by some external force; -- sometimes called vis inertiæ.

[Sarah]

Simple terms: The 'reason' that to why you have to use some sort of effort to move or stop something like an object.

The law/principle of inertia states that a body at rest will remain at rest and a body in motion will continue moving with a constant velocity unless acted upon by an external non zero force.

Don't confuse this with [momentum]

[Sarah]

when you can't get off the couch.

[Sarah]

Tendency for a person to resist a change in movement; Force needed to generate the momentum to cause movement

[Sarah]

Boostbuddy line of performance and making your slow car fast

[Dianne]

Inertia in Swimming. A resistance to movement.