A bouncing ball captured with a<unk> c flash at 25 images per second. A strobe light flashing at the proper period can appear to freeze or reverse cyclical motion A<unk> , also known as a strobe, is an instrument used to make a cyclically moving object appear to be slow-moving, or stationary. It consists of either a rotating disk with slots or holes or a lamp such as a flashtube which produces brief repetitive flashes of light. Usually, the rate of the<unk>  is adjustable to different frequencies. When a rotating or vibrating object is observed with the<unk>  at its vibration frequency (or a submultiple of it), it appears stationary. Thus<unk> s are also used to measure frequency. The principle is used for the study of rotating, reciprocating, oscillating or vibrating objects. Machine parts and vibrating string are common examples. A<unk>  used to set the ignition timing of internal combustion engines is called a timing light.
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