PHYS_111_Prell_lmtucker_Physics_si_uniform_circular_motion.pptx

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1. Physics si Uniform Circular Motion

2. Equations: Ac= Delta v / delta t Ac= v^2 / r Fc = m Ac V of cm = 2 pie r / T T= time for 1 rotation

3. Concept Check 1. Which vector represents the direction of the force vector when the object is located at point A on the circle?

4. Answer: The force vector is directed inwards to the circle, with is downwards relative to A

5. Concept Checker: Rex Things and Doris Locked are out on a date. Rex makes a rapid right-hand turn. Doris begins sliding across the vinyl seat and collides with Rex. To break the awkwardness of the situation, Rex and Doris begin discussing the physics of the motion that was just experienced. Rex suggests that objects which move in a circle experience an outward force. Thus, as the turn was made, Doris experienced an outward force that pushed her towards Rex.  Do you agree or disagree? Why?

6. Answer: Disagree Objects moving in a circle experience an inward force, exerted by the Rex Or she would continue to in a straight line and not stay in the vehicle She initially moved outward because there was nothing pushing her in so she kept moving until a force pushed her in

7. Last one. Kara Lott is practicing winter driving in the GBS parking lot. Kara turns the wheel to make a left-hand turn but her car continues in a straight line across the ice. Why??

8. Answer: A car turns in a circle due to the friction against its turned wheels. With wheels turned and no friction, there would be no circle. That is the problem in this situation.

9. Problem 1: A 900-kg car moving at 10 m/s takes a turn around a circle with a radius of 25.0 m. Determine the acceleration and the net force acting upon the car.

10. Solution: A= 4 m/s^2, F= 3600 N a  = v 2  / Ra = (10.0 m/s) 2  / (25.0 m) a = (100 m 2 /s 2 ) / (25.0 m) a = 4 m/s 2 F net  = m • a F net  = (900 kg) • (4 m/s 2 ) F net  = 3600 N

11. Problem 2 : A 95-kg halfback makes a turn on the football field. The halfback sweeps out a path that is a portion of a circle with a radius of 12-meters. The halfback makes a quarter of a turn around the circle in 2.1 seconds. Determine the speed, acceleration and net force acting upon the halfback.

12. Solution: v = d / tv = (0.25 • 2 • pi • R) / t v = (0.25 • 2 • 3.14 • 12.0 m) / (2.1 s) v = 8.97 m/s a = v 2  / Ra = (8.97 m/s) 2  / (12.0 m) a = (80.5 m 2 /s 2 ) / (12.0 m) a = 6.71 m/s 2 F net  = m*a F net  = (95.0 kg)*(6.71 m/s 2 ) F net  = 637 N

13. Last Problem: Determine the centripetal force acting upon a 40-kg child who makes 10 revolutions around the Cliffhanger in 29.3 seconds. The radius of the barrel is 2.90 meters.

14. Solution: F net  = 533 N Given : m = 40 kg; R = 2.90 m; T = 2.93s ( since 10 cycles takes 29.3 s). speed =(2 • pi • R) / T = 6.22 m/s . a = v 2  / R = = (6.22 m/s) 2  / (2.90 m) = 13.3 m/s/s F net  = m • a F net   = 533 N.