Circular Motion: Centripetal force Chapter 8 Nov 5/6

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

Read Circular Motion 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

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

Study Figure 8.1 on page 123 Draw the figure below Explain the figure with rotational speed and tangential speed

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? Facts Outside horse (larger radius) The outside horse

Check for Understanding Topic 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? Facts 5m/s

Check for Understanding Topic 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 2 RPM because rotational speed is not affected by radius/distance

Recall Newton’s 1 st Law Topic Newton’s 1 st Law Facts Things in motion stay in motion, in a straight line and at a constant speed unless an outside force acts on it

What makes objectives move in a circle? Topic Centripetal force Facts Means center-seeking Pulls toward center of circle Outside 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

HONORS- What makes objectives move in a circle? Topic Centripetal force Facts Centripetal force= mass x centripetal acceleration F c = ma c or F c = mv 2 r because a c = v 2 r

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

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

Closing Topic Why do objects move in a circle? Include the following terms in your explanation. Newton’s 1 st law Centripetal force Tangential speed Facts

Homework Read Chapter 9- page 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