In physics, length contraction – according to Hendrik Lorentz – is the physical phenomenon of a decrease in length detected by an observer of objects that travel at any non-zero velocity relative to that observer. This contraction (more formally called Lorentz contraction or Lorentz–Fitzgerald contraction) is usually only noticeable at a substantial fraction of the speed of light; the contraction is only in the direction parallel to the direction in which the observed body is travelling. This effect is negligible at everyday speeds, and can be ignored for all regular purposes. Only at greater speeds does it become important. At a speed of 13,400,000 m/s (30 million mph, .0447c), the length is 99.9% of the length at rest; at a speed of 42,300,000 m/s (95 million mph, .141c), the length is still 99%. As the magnitude of the velocity approaches the speed of light, the effect becomes dominant.