Terminal velocity facts for kids

Terminal velocity is the speed when an object falling through a fluid (usually air) is no longer getting faster.

Terminal velocity happens at the moment in time that the force of gravity, called weight, is the same as the opposite force of air resistance or friction. In other words, terminal velocity is the point at which the velocity (speed of moving of the falling object) is no longer getting greater. The gravitational force minus the force of drag (or air resistance) equals zero.

An object continues to fall steadily until air resistance becomes so great that it equals the pull of gravity and the object can fall no faster. Besides weight, terminal velocity depends on other factors such as shape and cross sectional area.

Example

The terminal velocity of a skydiver in a belly-to-earth (i.e., face down) free-fall position is about 195 km/h (122 mph or 54 m/s). This velocity is the limit of the acceleration process. The forces on the body balance each other more and more closely as the terminal velocity is approached. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on.

Higher speeds are achieved if the skydiver pulls in his or her limbs (see also freeflying). In this case, the terminal velocity increases to about 320 km/h (200 mph or 90 m/s), which is almost the terminal velocity of the Peregrine Falcon diving down on its prey.

Images for kids

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  Settling velocity Ws of a sand grain (diameter d, density 2650 kg/m3) in water at 20 °C, computed with the formula of Soulsby (1997).