Glossary
friction
Friction is the force that opposes motion when two surfaces are in contact. It turns movement into heat, and it depends on the surfaces and how hard they are pressed together.
Friction is the force that opposes motion when two surfaces are in contact. It turns movement into heat, which is why brakes slow a car, a saw blade warms up and your palms feel hot after rubbing them together.
It depends on the surfaces and on how hard they are pressed together: a rougher surface and a heavier load mean more friction, while the area of contact matters far less than most people expect. Starting friction is greater than sliding friction, which is why a heavy box is hardest to get moving and easier once it is sliding.
Friction is not simply the enemy. Without it you could not walk, brake, drive or trust a nail to stay in a wall; it is the reason a wedge holds, a belt drives a pulley and a tire grips the road. Where it is unwanted, it is reduced by lubricating, polishing, or replacing sliding contact with rolling contact — bearings and wheels.
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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)