Centripetal Force

For a particle in uniform circular motion (constant speed, radius $r$), the centripetal acceleration is $a=\dfrac{v^2}{r}$, directed toward the centre of the circle. By Newton's second law, there must therefore be a force of exactly this magnitude, also directed toward the centre — called the centripetal force:

("Centripetal" literally means "centre-seeking".)

Examples:

1. In a whirling stone on a string, the string tension provides the centripetal force.
2. In a satellite orbiting the Earth, the Earth's gravitational force provides it.
3. In a car turning on a road, friction between the tyres and the road provides it.
4. In a planet orbiting the Sun, the Sun's gravity provides it. …