Centripetal Force

1. Centripetal Force Section 5.3

2. 5.3 Centripetal Force • Newton’s 2nd Law • Whenever there is acceleration there is a force to cause it • F = ma • Fc = mac

3. WARNING!!! • Centripetal Force is not a new, separate force created by nature! • Some other force creates centripetal force • Swinging something from a string  tension • Satellite in orbit  gravity • Car going around curve  friction

4. Example • A 1.25-kg toy airplane is attached to a string and swung in a circle with radius = 0.50 m. What was the centripetal force for a speed of 20 m/s? What provides the Fc? • Fc = 1000 N • Tension in the string

5. Conceptual Problem • What affects Fc more: a change in mass, a change in radius, or a change in speed? • A change in speed since it is squared and the others aren’t.

6. Conceptual Example • During a circus trapeze act, a man hangs from a bar and swings his partner from their arms. Which is harder to do: hold the partner still under the bar, or to swing the partner under the bar? • Swing because not only is there gravity, but there is also centripetal force. • What provides the Fc? • Tension their arms

7. Example • Compare the maximum speeds a car can go around curve (r = 75 m) in dry weather s = 0.80 and in ice s = 0.10. • Dry  v = 24.2 m/s • Ice  v = 8.6 m/s

8. Conceptual Example Remember the good old days when cars were big, the seats were vinyl bench seats, and there were no seat belts? Well when I guy would take a girl out on a date and he wanted to get cozy, he would put his arm on the back of the seat then make a right hand turn. The car and the guy would turn since the tires and steering wheel provided the centripetal force. The friction between the seat and the girl was not enough, so the girl would continue in a straight path while the car turned underneath her. She would end up in the guy’s arms.

9. Practice Problems • Try to bend your mind around these. • 142 CQ 6 – 11, P11, 12, 14, 16, 17 • Total of 11 Problems