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Uniform Circular Motion

Uniform Circular Motion. Describing the motion of objects following a circular path. Vocabulary. Cycle One complete trip around the circumference of a circle Axis Center of rotation Period The time to complete one revolution or one cycle. Measured in seconds, symbol: T

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Uniform Circular Motion

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  1. Uniform Circular Motion Describing the motion of objects following a circular path.

  2. Vocabulary Cycle One complete trip around the circumference of a circle Axis Center of rotation Period The time to complete one revolution or one cycle. Measured in seconds, symbol:T Rotation Turning about an internal axis. (Earth rotates) Revolution Turning about an external axis. (Earth revolves around the sun)

  3. Two for you to try What is the period of rotation of the earth? What is the period of revolution of the earth? T = the time it takes to go around its axis once T = 24 hours T = the time it takes to go around the sun T = 1 year

  4. Uniform Circular Motion Object moves in a circle at a constant speed.

  5. Velocity A car travels clockwise (CW) around a track at a constant speed. Draw the tangential velocity, vt, vectors at 3 locations. vt Note: vectors are the same length (magnitude) but direction is different. vt vt

  6. Acceleration Centripetal Center seeking Centripetal acceleration is directed towards the center along the radius of the circle. ac An object in UCM is always accelerating. V is not constant.

  7. Acceleration A car travels counter clockwise (CCW) around a track at a constant speed. Draw the centripetal acceleration, ac,vectors at 3 locations. vt ac vt ac ac vt

  8. REMEMBER… F=ma? • Well… in circular motion • a = v2/r • So… Fc = ____________

  9. Centripetal Force The cause of the circular motion Examples: string tension, gravity, washing machine basket in the spin cycle. Toward the center!

  10. Fc Fc Fc

  11. Centripetal Force If the centripetal force ceases to act, the object follows the tangential velocity and flies of tangent to the circle. “Centrifugal Force” a fictitious force due to a non-inertial frame of reference. Remember the movie: what you think is opposite reality

  12. Example Find the speed of a person on Earth’s equator. a = 9.8 m/s2 re = 6.37 X 106 m

  13. Another Example A ball with a mass of 5 kg tied to a rope is being swung around in the air at a speed of 15 m/s and the string length from hand to the ball is 1.2m. Find the acceleration and centripetal force.

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