Objects can ROTATE like the earth on its own axis.

Rotate: turn about an internal axis

Objects can REVOLVE like people on a ride at Great America.

Revolution: turn aboutan external axis.

Objects can also do both at the same time: Like the planets in our solar system.

The planets REVOLVE around the sun andROTATE about their own axis.

What rides at Great America do both?

Our lesson for this session will only deal with revolutions on a circle. No rotations.

As the lady bug revolves around The circle what do you notice aboutThe velocity vector? What do you notice about theAcceleration vector?

The velocity vector is always a straight line or linear off the circle. This is a tangent line. So this type of velocity is called linear or tangential velocity.

The acceleration vector always points toward the center. This is called centripetal acceleration.

Now lets get active to learn about the following terms:1. Angular velocity, 2. tangential velocity, 3. Centripetal acceleration

Go to the website and click on the ladybug animation.Have your guided practice available so you can use the animation and collect some pieces of information.

http://www.cabrillo.edu/~jmccullough/Physics/Circular_Motion.html#Anchor-Studen-33324

Centripetal means “center-seeking” and centripetal force is nota new special kind of force. It comes in many forms such as tensionand friction.

Objects moving in a circle experience a center seeking force called centripetal force.

When the bucket is at the top of the circle it does not fallout. Why not? The answer is in Newton’s First Law.Think inertia. The FORCE on the bucket IS toward the center.

The tether ball’s tension in the rope is divided into an upwardY force and a center-seeking x force. So the x force is the Centripetal force.

Centripetal force

No matter where the car is on the curve it will experience the center seeking force called centripetal force.

Friction keeps the car on the curve.If there was no friction which way would the car slide?

The friction is the centripetal force.

Remember Newton’s Second Law? F = m x a

This applies to circular motion as well except that the acceleration has a different formula because its circular motion.

So for circular motion F = m * ( v2 / r ) F = forcem = massv = linear (tangential velocity) r = radius of circle.

A 5 kg object rotates on a string with a velocity of 3 m/s and a radius of 1.5 m. What is

the force on the object? F = m * v2 /r m = 5 kg v = 3 m/s r = 1.5 m F = 5 * 32/1.5 Ans: 30 N