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. metre per second squared. (Note: Shock wave is sometimes abbreviated as shock when the context is clear.)

Sometimes, for convenience, the magnitude of a shock is stated as a multiple of the standard 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/s².

The italic symbol g used above must not be confused with the upright symbol g meaning gram.

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