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Lesson 11 – Uniform Circular Motion

Lesson 11 – Uniform Circular Motion. 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 ?.

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Lesson 11 – Uniform Circular Motion

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  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 • Instantaneous acceleration of uniform circular motion is directed toward the centre of the circle • This can be illustrated by recalling the definition of instantaneous acceleration:

  6. Direction of Instantaneous Acceleration If we only focus on the direction of we can see that as , the vector starts approaching the vector and the vector points towards the center of the circle

  7. Magnitude of Centripetal Acceleration • The magnitude of centripetal acceleration is quantified by the following 3 equations: Where: is the magnitude of the centripetal acceleration (m/s2) is the period (s) is the speed (m/s) is the radius (m) is the frequency (Hz)

  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. • Find the mean orbital speed of the Moon. • 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. • Which rate of rotation gives the greater speed for the stone at the end of the sling? • What is the centripetal acceleration of the stone at 8.00 rev/s? • What is the centripetal acceleration at 6.00 rev/s?

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

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