# Lecture 16 Chapter 6: Circular Motion Please sit in the first six rows.

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Lecture 16 Chapter 6: Circular Motion Please sit in the first six rows

Quick Review of Last Friday Last Friday The kinematics of uniform circular motion TODAY – The dynamics of uniform circular motion – Circular orbits of satellites – Newton’s law of gravity

Uniform Circular Motion Uniform magnitude of velocity (speed) is constant

Going from angular velocity to angular displacement:

Uniform Circular Motion Uniform magnitude of velocity (speed) ω, is constant But α is not zero because direction of velocity is changing.

Centrifugal Force NOT A REAL FORCE What supplies the force to make your acceleration such as to cause you to move in a circle? Centripetal FORCE—towards the center. This is the real force involved. v a

Vertical Circle Ferris wheel—free body diagram when at top F NET w=mg n TOP

Ferris Wheel At the bottom “Apparent weight” = n is greater at bottom of cycle than at top n BOTTOM w=mg

Centrifuges Diameter = 18 cm Centripetal acceleration = 250,000 g What is the frequency? Rev/sec and rpm Apparent weight of a 3 mg mass in this machine?

Workbook due today Go to board and explain – 1a and c – 1b and d – 2 – 3 – 4 – 5 – 6a,b and c

A cyclist goes around a circular track at constant speed. Since her speed is constant, her acceleration is zero 1.True 2.False 3.Need more information

6.15 A 1500 kg car drives around a flat 200m diameter circular track. What are the magnitude and direction of the net force on the car? What causes this force?

When a ball on the end of a string is swung in a vertical circle: What is the direction of the acceleration of the ball? 1.Tangent to the circle, in the direction of the ball’s motion 2.Toward the center of the circle