1. Uniform Circular Motion Definition: the motion of an object in a circular path with a constant speed Homework: Read pages 153 – 156 P 156 Answer questions: 12, 13, 14, 15

2. When does this happen? Driving a car at constant speed around a circular corner OR

3. Speed in a circular path Recall: to find speed V = distance / time for a circular path d = 2  r the time required to complete one full revolution is called the period (T) Therefore, v = 2  r / T

4. Constant speed, but what about velocity? Velocity of an object undergoing UCM is always directed tangent to the circular path Direction is constantly changing, velocity is not constant Therefore, the object must be accelerating

5. Centripetal Acceleration Acceleration experienced by an object moving in a circular path at a constant speed. Directed to the center of the circular path centripetal means “center seeking” a c = V 2 / r

6. Centripetal Force Force directed toward the center of the circular path Causes the centripetal acceleration F c = m a c

7. Do Now Assume that the moon orbits the Earth in a circular orbit in 27.32 days. Using the List of Physical Constants on your Reference Tables, calculate the following: a.the speed of the moon in its orbit. b.the centripetal acceleration experienced by the moon c.the centripetal force that keeps the moon in its orbit.

8. The answers: a.V = 1022 m/s b.a c = 0.00272 m/s 2 c.2.0 x 10 20 N