A shake is an informal unit of time equal to 10 nanoseconds, or 10⁻⁸seconds. It has applications in nuclear physics, helping to conveniently express the timing of various events in a nuclear explosion. The typical time required for one step in the chain reaction (i.e. the typical time for each neutron to cause a fission event which releases more neutrons) is of order 1 shake, and the chain reaction is typically complete by 50 to 100 shakes.

This is also applicable to circuits. Since signal progression in IC chips is very rapid, on the order of nanoseconds, a shake is good measure on how quickly a signal can progress through an IC.

Like many nuclear units, it is derived from Top Secret operations of the Manhattan Project during World War II. The word comes from the expression "two shakes of a lamb's tail," which indicates a very short time interval. For nuclear-bomb designers, 10 nanoseconds was a convenient specific interval to connect to this term.

Shake may refer to:

Unit may refer to: