2. Physics I Honors Specific Forces Centripetal Force

3. Physics I Honors Warm up Planet Zonk is twice as far from the sun as Earth. What is its period? Herman the astronaut ( mass 80kg) is floating in orbit about earth and feels a gravitational attraction of 360 newtons. What is the value of gravity at his location? What is his orbital radius as a multiple of earth’s radius.

4. Physics I Honors Objectives · Explain why a body moving with uniform circular motion must be regarded as undergoing acceleration and state the direction of the acceleration. · Predict the path of an object which has a force acting on it perpendicular to the direction of its velocity. · Indicate the direction of the instantaneous velocity, centripetal acceleration, and centripetal force for an object moving at constant velocity in a circle. · Calculate centripetal acceleration and force.

5. Physics I Honors Imagine… Think about the moon on its journey around the earth… How about an amusement park ride that spins you around in a constant circle… How do you describe this kind of circular motion? Is the velocity constant or is it accelerating? How does the moon stay up there in the sky?

6. Physics I Honors What Is Uniform Circular Motion? Uniform Circular Motion is motion in a circle with: –Constant Radius R v – Constant Speed v = |v|

7. Physics I Honors What if the String Breaks?

8. Physics I Honors Centripetal Force Provides acceleration toward the center which causes an object to continually change velocity because it is changing direction while the speed remains constant. F c = ma c

9. Physics I Honors What happens when you turn.

10. Physics I Honors Without Centripetal Force

11. Physics I Honors With Centripetal Force

12. Physics I Honors Force is Perpendicular to the Velocity

13. Physics I Honors Check your understanding An object is moving in a clockwise direction around a circle at constant speed. Use your understanding of the concepts of velocity, acceleration, and force to answer the next five questions. Use the diagram shown at the right. A B C

14. Physics I Honors Vector 1 1. Which vector below represents the direction of the force vector when the object is located at point A on the circle?

15. Physics I Honors Vector 2 2. Which vector below represents the direction of the force vector when the object is located at point C on the circle?

16. Physics I Honors Vector 3 Which vector below represents the direction of the velocity vector when the object is located at point B on the circle?

17. Physics I Honors Vector 4 4. Which vector below represents the direction of the velocity vector when the object is located at point C on the circle?

18. Physics I Honors Vector 5 5. Which vector below represents the direction of the acceleration vector when the object is located at point B on the circle?

19. Physics I Honors Motion in a circle Velocity is a vector; it has direction An object travelling in a circle at constant speed is continuously changing direction Therefore, it is accelerating Thus, requires a force

20. Physics I Honors Centripetal Acceleration This acceleration can be calculated a c = v 2 / r a is the centripetal acceleration v is the speed r is the radius of the circle

21. Physics I Honors Circular Speed As speed is distance traveled divided by the time it takes to travel the distance v = 2  r/T v is the speed r is the radius of the circle T is the period of revolution

22. Physics I Honors Practice 1 A runner moving at a speed of 8.8 m/s rounds a bend with a radius of 25 m. What is the centripetal acceleration of the runner? 3.1 m/s 2 What provided this acceleration to the runner? friction between his shoes and the track

23. Physics I Honors Practice 2 Racing on a flat track, a car going 32 m/s rounds a curve 56 m in radius. What is the car’s centripetal acceleration? 18 m/s 2 What would be the minimum coefficient of static friction between tires and road that would be needed for the car to round the curve without skidding? 1.8

24. Physics I Honors Homework A/c # 6 and 7 Problems 13 to 20