lecture chapter 6 part 2, circular motion

# lecture chapter 6 part 2, circular motion - Circular motion...

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8 Circular motion planet, string and a ball, key chain. . F net 0, because v is not constant, a 0. a =? Centripetal acceleration a cp = r is radius of circle v is the velocity at that point See the figure on textbook. Acceleration direction- toward the circle center. Constantly changing direction of v . Acceleration direction also keeps changing. To do circular motion object Needs centripetal a cp Total force in radius direction = m a cp = m This total force in radius direction has a fancy name: Centripetal force. Σ F= ma Σ F r = m a cp =F net r = F cp F net r = m v 2 /r r v 2 r v 2 Centripetal force is not a new force. It is simply the total force in radius direction.

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9 Σ Fr = T sin θ = m v 2 /r F net or F cp is the required (needed) net force (force sum) along the radius direction of circular motion, it is not another new force. You should find which existing forces provide a cp F net r = F cp =m v 2 /r You should never add F cp to existing forces. Centripetal force can be tension or gravity, or friction, or normal force or combination of any of these real forces, which keep object in circular orbit. Σ Fr = f s = m v 2 /r Examples: Planets and moons in orbit F cp = gravity On roller coaster: F cp depends on position…. (at the bottom F cp = N –mg, on the top inside the track F cp = N + mg …)
10 mv 2 /r , is needed net force toward center, V increases, F cp needed ; easier to fly off orbit r big., F cp needed small; easier to stay in orbit

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## This note was uploaded on 08/25/2010 for the course PHYS 111 taught by Professor Jamesm.lockhart during the Spring '09 term at S.F. State.

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lecture chapter 6 part 2, circular motion - Circular motion...

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