In mechanics, a shock is a sudden acceleration or deceleration caused, for example, by impact or explosion. Shock is measured in the same units as acceleration, i.e. meters per second per second.

Sometimes, for convenience, the magnitude of a shock is stated as a multiple of the acceleration due to free fall in the Earth's gravity, a quantity with the symbol g having the value 9.80665 m·s-2. Thus a shock of "2g" is equivalent to about 19.6 m·s-2.

The symbol g used above must not be confused with the same symbol g meaning gram, 1/1000th of a kilogram.

A variety of shock absorbers are used to reduce the strength of shocks in machinery.