Glossary
clutch
The clutch connects and disconnects the engine from the transmission. Press the pedal and the friction surfaces separate, so the engine can keep turning while gears are changed.
The clutch is the coupling that connects and disconnects the engine from the transmission. Press the pedal and the two friction surfaces separate, so the engine keeps turning while the gearbox and wheels are free to change gear.
It works by friction. A disc lined with friction material is clamped between the engine's flywheel and a spring-loaded pressure plate. With the pedal released, that sandwich locks the engine's output to the gearbox input and drives the wheels; with the pedal pressed, the surfaces slip apart and no power reaches them.
It is also how a car gets moving from rest: the driver lets the clutch out gradually so the engine and the wheels meet each other a little at a time, which is why riding the pedal to hold a car on a hill wears the disc out. A worn clutch slips under load, and the engine speeds up without the car accelerating.
Taught in
Related terms
- transmission — The transmission is the gearbox between the engine and the wheels. It matches the engine's narrow speed range to the wide range the vehicle needs, trading revolutions for torque.
Source: Official ASVAB — subtest descriptions (what each subtest asks) and the CAT-ASVAB scored-question counts (accessed 2026-09)