Relativistic speed
Relativistic speed refers to speed at which relativistic effects become significant to the desired accuracy of measurement of the phenomenon being observed. Relativistic effects are those discrepancies between values calculated by models considering and not considering relativity. Related words are velocity, rapidity, and celerity which is proper velocity. Speed is a scalar, being the magnitude of the velocity vector which in relativity is the four-velocity and in three-dimension Euclidean space a three-velocity. Speed is empirically measured as average speed, although current devices in common use can estimate speed over very small intervals and closely approximate instantaneous speed. Non-relativistic discrepancies include cosine error which occurs in speed detection devices when only one scalar component of the three-velocity is measured and the Doppler effect which may affect observations of wavelength and frequency.Relativistic effects are highly non-linear and for everyday purposes are insignificant because the Newtonian model closely approximates the relativity model. In special relativity the Lorentz factor is a measure of time dilation, length contraction and relativistic mass increase of a moving object.
Speed (comics)
Speed is a mutant with the power to move and accelerate at speeds far beyond those of normal human beings. His physiology is designed to move at high speeds which also grants him superhuman reflexes, agility, and durability. This durability is limited to impact forces, so bullets, energy blasts, and other piercing attacks are capable of harming him. It is also likely that Speed possesses a high amount of superhuman strength in his lower body, allowing him to lift around 1 ton, while his upper body is strengthened to the point where he can lift around 800 lbs. Although his top speed is unknown, he can exceed the speed of sound (about 1,225 km/h, or 761 mph) and resist the effects of friction, reduced oxygen, and kinetic impact while moving at those speeds. In "Young Avengers Presents" #3 he asserts that he is "Quicksilver fast", shown running from the eastern seaboard of the United States to Genosha, an island off the east coast of Africa, as well as search the entire island for anyone living there in the same amount of time it takes Wiccan to teleport the same distance. This indicates that Speed is fast enough to run across the surface tension of a body of water without sinking. In addition, his mind can operate in an accelerated state, allowing him to read in super speed and remember everything he's seen.