Circular MotionMotion that repeats itself is called periodic motion.

Projectile motion–since it doesn’t repeat–is not periodic. The motion of a swinging ball is an example of circular

motion – which is periodic. Another example is a planet orbiting around the sun (see below).

Circular MotionLet’s look closer at the planet below…

An object in circular motion always tries to travel in a __________ __________ (Newton’s 1st Law).

In order for the object to travel in a circle, there must be a force that “holds” it in orbit – a force that acts toward

the center of the motion. This force is called the ___________________.

Circular MotionLet’s look closer at the planet below…

An object in circular motion always tries to travel in a __________ __________ (Newton’s 1st Law).

In order for the object to travel in a circle, there must be a force that “holds” it in orbit – a force that acts toward

the center of the motion. This force is called the CENTRIPETAL FORCE.

Circular MotionCentripetal force could be frictional, gravitational, or tensile…but we simply call it the centripetal force, Fc.

Fc always acts toward the center of the circular motion (centripetal actually means “center-seeking”).

(think of the stopper demo…What was holding the stopper in orbit? _________

And in what direction was it pulling the stopper? _____________)

Circular MotionOur focus will be on uniform circular motion (meaning that the object is traveling at a constant speed). But

since the object is constantly changing direction, it has a different velocity at every moment. And since the

object’s velocity is changing, that means the object is _____________.

This is call the Centripetal ________________.

Circular MotionCentripetal Acceleration always acts in the same

direction as the centripetal force.

Fc = mac ac = v2/r

So… Fc = (m v2)/r