The Engineers Vice
The engineers vice uses the lever principnciple uses a small force to exert a large compressive force to an object enclosed in a vice.
\Suppose the vice handle is turned with a forc F and produces a force f to compress the captive of the screw. Equating work done by F to the work done by the vice gives
This derived expression assumes the vice has no friction (which of course is impossible). The same calculation can be applied to find the force needed on the handle of a car jack to lift one corner of a car so a wheell can be changed. A car weighs typically between 1,000 – 2,000 kg and these wieghts can obviously not be lifted unaided and held steady so that a wheel can be changed.