1. Circular Motion Motion 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).

2. Circular Motion Let’s look closer at the planet below… An object in circular motion always tries to travel in a __________ __________ (Newton’s 1 st 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 ___________________.

3. Circular Motion Let’s look closer at the planet below… An object in circular motion always tries to travel in a __________ __________ (Newton’s 1 st 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.

4. Circular Motion Centripetal force could be frictional, gravitational, or tensile…but we simply call it the centripetal force, F c. F c 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? _____________)

5. Circular Motion Our 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 ________________.

6. Circular Motion Centripetal Acceleration always acts in the same direction as the centripetal force. F c = ma c a c = v 2 /r So… F c = (m v 2 )/r