centripetal force

the force, acting upon a body moving along a curved path, that is directed toward the center of curvature of the path and constrains the body to the path.


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World English Dictionary
centripetal force
Compare centrifugal force a force that acts inwards on any body that rotates or moves along a curved path and is directed towards the centre of curvature of the path or the axis of rotation

Collins English Dictionary - Complete & Unabridged 10th Edition
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Word Origin & History

centripetal force
1709, from centripetal. Fig. use is from 1711. Used in Mod.L. 1687 by Newton in "Principia" (vim ... centripetam).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
centripetal force  

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A force acting on a moving body at an angle to the direction of motion, tending to make the body follow a circular or curved path. The force of gravity acting on a satellite in orbit is an example of a centripetal force; the friction of the tires of a car making a turn similarly provides centripetal force on the car.

Our Living Language  : In a popular carnival ride, people stand with their backs against the wall of a cylindrical chamber. The chamber spins rapidly, the floor drops out, but the riders remain pressed against the wall without falling. Although the riders may insist they stay aboard because of an outward force pushing them against the wall, the reality is the opposite: the riders are subject to an inward, or centripetal, force. As the ride spins, it forces the riders to travel in a circle. According to Isaac Newton's law of inertia, objects in motion tend to travel in a straight line at constant speed unless acted on by an external force. To make an object travel along a curved path, a force must keep the object moving toward the center of curvature—in this case the axis of rotation. The wall of the ride's cylindrical chamber accomplishes this by pushing the riders toward the center (with the friction between the riders and the wall holding the riders up). The force of the Earth's gravity acts as a centripetal force on orbiting objects, such as the Earth's Moon, which is constantly being accelerated toward the center of the Earth, as in free fall. The Moon has enough inertia not to plummet into the Earth but not so much that it can escape the Earth's pull, and thus it will orbit almost indefinitely.
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