Glossary
inertia
Inertia is an object's resistance to any change in its motion; it grows with mass, so the heavier object is the harder one to start, stop or turn.
Inertia is the tendency of an object to keep doing what it is already doing — to stay at rest, or to keep moving in a straight line at a constant speed, unless a force acts on it. It is not a force and it is not a measure of speed: it is how much an object resists being changed, and it grows with mass. Ten times the mass means ten times the resistance to being accelerated, stopped or turned.
The subtest usually asks it as a comparison, so find the heaviest object and that is the answer. It also hides inside two traps. Momentum is mass times velocity, so a heavy slow object and a light fast one can carry equal momentum while the heavy one still has the greater inertia. Weight is gravity's pull on a mass, so on the Moon the weight changes and the inertia does not.
Inertia is also why a load in a truck keeps moving when the truck brakes, and why a heavy flywheel carries an engine through the stroke between power pulses.
Taught in
Related terms
- mechanical advantage — Mechanical advantage is how much a machine multiplies the force you apply: a lever, gear or pulley trades distance for force, so a small effort raises a large load.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)