Knowledge you can walk. Read the idea below, then step up to the general, across to peers or down to the specific.
Physical
Circular Motion
Circular motion is the movement of an object along a circular path, which always needs a force pointing toward the center.
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The idea
Circular motion is the motion of an object along a circular path. A stone whirled on a string, a car going around a curve and a point on a turning wheel all move this way. So do the blades of a ceiling fan spinning around their hub and a satellite traveling in a circular orbit around Earth.
Circular motion can be uniform, meaning the speed stays constant, or non-uniform, meaning the speed changes. Even in uniform circular motion the object is accelerating, because its velocity keeps changing direction. This acceleration points toward the center of the circle and is called centripetal acceleration. Producing it requires a force directed toward the center, called centripetal force. For a stone on a string, the tension in the string supplies that force, and for a car on a curve, friction between the tires and the road does.
According to Newton's laws of motion, an object without centripetal acceleration would travel in a straight line. That is why a whirled stone flies off in a straight line when its string snaps. The same idea describes a solid object rotating about a fixed axis, where every point on the object moves in its own circle around that axis.
Check yourself
Question 1 of 2
What is the inward acceleration of an object moving in a circle called?
Composition
what it's made of
- Circular path — The round route the object follows around a center point.
- Speed — Constant in uniform circular motion and changing in non-uniform circular motion.
- Changing velocity — The direction of motion changes at every moment, even when the speed does not.
- Centripetal acceleration — The acceleration toward the center of the circle.
- Centripetal force — The force toward the center that produces centripetal acceleration.
Connection
how it relates
Under Motion
Change
how and why it evolves
- Past
- Before Isaac Newton, many thinkers treated circular motion, such as the movement of the heavens, as natural and needing no force. Newton's laws of motion showed that an object left alone moves in a straight line, so any curved path requires a force.
- Now
- Engineers use centripetal force calculations to design curved roads, amusement park rides and spinning machines such as centrifuges.
- Next
- As more satellites are launched, calculating circular and nearly circular orbits will likely matter even more for keeping them on course and avoiding collisions.