1. Lesson 11 – Uniform Circular Motion

2. Minds-On *this slide is not intended to be shown in class Do the “Swing a plate with a cup of water over your head” demo. Ask students what keeps the water moving in a circle? If the plate broke free, where would the plate and water go?

3. Uniform Circular Motion Uniform Circular Motion is motion that occurs when an object has constant speed and constant radius Imagine you have attached a rubber stopper to the end of a string and are whirling the stopper around your head in a horizontal circle

4. Centripetal Acceleration An object in uniform circular motion is accelerating. Even though the speed is constant the vector direction of velocity is constantly changing. This type of acceleration is referred to as Centripetal Acceleration.

5. Direction of Instantaneous Acceleration

7. Magnitude of Centripetal Acceleration

8. Example 1 The orbit of the Moon about the Earth is approximately circular, with a mean radius of 3.84 x 108 m. It takes 27.3 days for the moon to complete one revolution about the Earth. a)Find the mean orbital speed of the Moon. b)Its centripetal acceleration.

9. Example 2 David found that he can revolve a sling of length 0.600 m at the rate of 8.00 rev/s to hit Goliath. He then noticed that if he increased the length to 0.900 m, he could revolve the sling only 6.00 times per second. a)Which rate of rotation gives the greater speed for the stone at the end of the sling? b)What is the centripetal acceleration of the stone at 8.00 rev/s? c)What is the centripetal acceleration at 6.00 rev/s?

10. Homework Nelson Physics 12 (2001) Textbook page 127 Questions 3, 5, 7, 8