1. Unit 6: Circular Motion Consider a Ferris wheel. ◦ The cars are in circular motion because they revolve about a single axis. ◦ The line about which the rotation occurs is called the axis of rotation.

2. Unit 6: Circular Motion Here’s a fun video:video

3. Unit 6: Circular Motion Tangential speed (v t ) can describe the speed of an object in circular motion. The tangential speed of a car on the Ferris wheel is the car’s speed along an imaginary line drawn tangent to the car’s circular path.

4. Unit 6: Circular Motion When tangential speed is constant, the motion is described as uniform circular motion. The tangential speed depends upon the distance from the object to the center of the circular path.

5. Unit 6: Circular Motion We know that the radius of the circle dictates speed (displacement over time). Think of running a lap of a track and having one runner in lane 1 and one runner in lane 6.

6. Unit 6: Circular Motion Even though the car on the Ferris wheel is moving at a constant speed, it is undergoing an acceleration. Change in velocity is a change in a vector which includes direction.

7. Unit 6: Circular Motion The acceleration directed toward the center of a circular path is called centripetal acceleration.

8. Unit 6: Circular Motion Example: A test car moves at a constant speed around a circular track. If the car is 48.2m from the track’s center and has a centripetal acceleration of 8.05 m/s 2, what is the car’s tangential speed? (19.7 m/s)

9. Unit 6: Circular Motion Consider a ball tied to a string that is being whirled around above your head. The inertia of the ball tends to maintain the balls motion in a straight path. The string, however, exerts a force that overcomes this tendency.

10. Unit 6: Circular Motion Forces on the ball are gravitational and the force exerted by the string. The force exerted by the string has horizontal and vertical components. The vertical component is equal and opposite to the gravitational force. The horizontal component is the net force and is directed toward the center of the circle.

11. Unit 6: Circular Motion The net force that is directed to the center of the circle is known as the centripetal force.

12. Unit 6: Circular Motion

13. Example: A pilot is flying a small plane at 56.6 m/s in a circular path with a radius of 188.5 m. The centripetal force needed to maintain the plane’s circular motion is 1.89x10 4 N. What is the plane’s mass? (1.11x10 3 kg)

14. Unit 6: Circular Motion Homework: Worksheet: Circular Motion