1. Circular Motion: Centripetal force Chapter 9 Nov 7/8

2. Objectives Develop examples of centripetal force Describe the motion of an object if the centripetal force acting on it ceases

3. Read section 9.2 on page 123 Topic What is tangential speed? What is rotational speed? Facts The linear component of something moving in a circle. Number of circles something makes in a certain amount of time

4. Difference between Tangential and Rotational speed Topic Tangential Speed Rotational speed Facts Depends on the circles radius – Larger radius = more speed – Smaller radius = less speed Does not depend on radius/distance Same no matter where on circle

5. Study Figure 9.3 on page 124 Draw the figure below Explain the figure with rotational speed and tangential speed

6. Check for Understanding Topic Which has a greater tangential (linear) speed travels faster on a merry-go- round, a horse on the outside or one near the center. Who will fall off the ride faster? The tangential speed at the outer rim of a Ferris wheel is 10 m/s. What is the tangential speed of a position half way from the center to the outer rim? You sit at the outer rim of a Ferris wheel that rotates at 2 revolutions per minute (RPM). What would your rotational speed be if you were instead clinging to a position halfway from the center to the outer rim? Facts Outside horse (larger radius) The outside horse 5m/s 2 RPM because rotational speed is not affected by radius/distance

7. What makes objectives move in a circle? Topic Centripetal force Facts Means center-seeking Any force that causes an object to follow a circular path Example: gravity pulls all of us to the center of the Earth Units are Newtons (N) Symbol is F c Centripetal force= mass x centripetal acceleration F c = ma c or F c = mv 2 r because a c = v 2 r

8. Teacher Demonstration Centripetal force and tangential speed Topic Why does the cup move in a circle? What will happen if I let the cup go? Facts Centripetal force pulls inward (from my hand) while tangential speed acts at each point resulting in the circle. The cup will fly in a straight line from the point the centripetal force stops

9. Check for Understanding Topic What would happen i f the force of gravity suddenly stopped acting on the planets? Facts They would fly off tangent in space, rather than continue their orbit

10. Closing Topic Why do objects move in a circle? Include the following terms in your explanation. Centripetal force Tangential speed Facts

11. Homework Read Chapter 12 This material is difficult to understand, but write notes and questions This will be checked for a HW grade It will also help you understand the next lesson