1. Do Now: (on index card) 1. How much time did you spend on physics HW this weekend? Are you satisfied with the amount of time/effort you are putting in this course? Are you currently up to date with all assigned HW? 2. A car traveling East at 15 mph maintains its speed as the driver makes a left turn. 2 seconds later the car is traveling north at 15 mph. Did the car accelerate? Explain.

2. Do Now (11/7): 1. What is acceleration? 2. A car traveling East at 15 mph maintains its speed as the driver makes a left turn. 2 seconds later the car is traveling north at 15 mph. Did the car accelerate? Explain. 3. *bonus – What team did the Ravens SWEEP last night?!?!?!

3. Acceleration Acceleration = change in velocity over time Acceleration = change in velocity over time Velocity represents speed AND direction – acceleration is a change in EITHER Velocity represents speed AND direction – acceleration is a change in EITHER

4. Circular Motion 11/7/11

5. Uniform Circular Motion Uniform circular motion: the motion of an object in a circle at a constant speed. Uniform circular motion: the motion of an object in a circle at a constant speed. http://www.physicsclassroom.com/ mmedia/circmot/ucm.cfm http://www.physicsclassroom.com/ mmedia/circmot/ucm.cfm http://www.physicsclassroom.com/ mmedia/circmot/ucm.cfm http://www.physicsclassroom.com/ mmedia/circmot/ucm.cfm

6. Speed Circumference = 2*pi*Radius Circumference = 2*pi*Radius v= 2πr/T v= 2πr/T T= period: the time it takes an object t0 revolve around the circle once T= period: the time it takes an object t0 revolve around the circle once

7. Speed Which orange dot moves fastest? Which orange dot moves fastest?

8. Velocity Vector Tangent: a line that touches a circle at one point but does not intersect it. Tangent: a line that touches a circle at one point but does not intersect it.

9. Example: A tube is placed upon the table and shaped into a three-quarters circle. A golf ball is pushed into the tube at one end at high speed. The ball rolls through the tube and exits at the opposite end. Describe the path of the golf ball as it exits the tube.

10. Centripetal Acceleration Centripetal acceleration: the acceleration of an object in circular motion; always points to the center of the circle Centripetal acceleration: the acceleration of an object in circular motion; always points to the center of the circle

11. Example #1 A merry-go-round has radius 5 m. If a boy sits on the edge of the merry-go- round traveling with a speed of 10 m/s, what is his centripetal acceleration?

12. Example #1 A merry-go-round with radius 5 m turning at a speed of 10 m/s. If a boy sits on the edge of the merry-go- round, what it his centripetal acceleration? A merry-go-round with radius 5 m turning at a speed of 10 m/s. If a boy sits on the edge of the merry-go- round, what it his centripetal acceleration? a c =v 2 /r=(10) 2 /5=20 m/s 2 a c =v 2 /r=(10) 2 /5=20 m/s 2

13. Practice: Please use the rest of class to work on the paper “Circular Motion.” It will be due Friday! Enjoy! Please use the rest of class to work on the paper “Circular Motion.” It will be due Friday! Enjoy!

14. Do Now (11/9): A 1400 kg sports car drives at a constant speed around an unbanked circular track with a radius of 300 m. The car completes one lap every 50 s. 1. What is the speed of the car? 2. Is the car accelerating? If yes, what is the magnitude and direction of the acceleration? Explain your answer. 3. What piece of information was unecessary? Why?

15. Do Now (11/9): A 1400 kg sports car drives at a constant speed around an unbanked circular track with a radius of 300 m. The car completes one lap every 50 s. 1. What is the speed of the car? 2. Is the car accelerating? Why or why not? 3. What piece of information was unecessary? Why?

16. Example #2 A merry-go-round with radius 5 m turning at a speed of 10 m/s. If a boy sits on the edge of the merry-go-round, what is the period? A merry-go-round with radius 5 m turning at a speed of 10 m/s. If a boy sits on the edge of the merry-go-round, what is the period?

17. Practice: Please use the rest of class to work on the paper “Circular Motion.” It will be due Friday! Enjoy! Please use the rest of class to work on the paper “Circular Motion.” It will be due Friday! Enjoy!

18. Do Now (11/10): A merry-go-round with radius 10 m turns at a speed of 15 m/s. If a boy sits on the edge of the ride, 1. What is the period? 2. Is he accelerating? If so, what is the magnitude and direction of his acceleration?

19. Classwork/Quiz Review (11/10): Please use the rest of class to work “Circular Motion Worksheet.” It will be due at the end of class TODAY! Enjoy! Please use the rest of class to work “Circular Motion Worksheet.” It will be due at the end of class TODAY! Enjoy!

20. Do Now (11/11): Determine the centripetal acceleration of a child who makes 20 revolutions on a merry-go-round in 80 seconds. The radius of the merry-go- round is 5 m.

21. Pass in Homework and Do Now’s (You should have 4), then clear your desk of everything except your notecard, calculator, and a writing utensil. Pass in Homework and Do Now’s (You should have 4), then clear your desk of everything except your notecard, calculator, and a writing utensil.

22. Do Now (11/14): A car drives horizontally off a wharf at 15 m/s. If the wharf is 25 m above water, calculate 1. the time of flight (mayhem). 2. the horizontal distance traveled.

23. Classwork/TEST Review (11/14): Please use the rest of class to work your test Review sheet. It will be due on Wenesday! Enjoy! Please use the rest of class to work your test Review sheet. It will be due on Wenesday! Enjoy!

24. Newton’s Second Law for Circular Motion F net =ma c =mv 2 /r F net =ma c =mv 2 /r

25. Centripetal Force F c = mv 2 /r F c = mv 2 /r

26. Example #2 A 9800 N car is driven on a circular track with a diameter of 400.0 m at 20.0 m/s. Calculate the car’s centripetal acceleration & its centripetal force. A 9800 N car is driven on a circular track with a diameter of 400.0 m at 20.0 m/s. Calculate the car’s centripetal acceleration & its centripetal force.

27. Unbalanced Forces Unbalanced forces cause objects to accelerate Unbalanced forces cause objects to accelerate

28. Example #3 What net force must act on a 5 kg mass that is moving at a constant speed of 4 m/s around a circle with a radius of 2 m? What net force must act on a 5 kg mass that is moving at a constant speed of 4 m/s around a circle with a radius of 2 m?

29. Example #4 A 1400 kg sports car drives at a constant speed around an unbanked circular track with a radius of 200 m. The car completes one lap every 63 s. 1. What is the speed of the car? 2. Is the car accelerating? If yes, what is the magnitude and direction of the acceleration? Explain your answer. 3. What is the minimum coefficient of friction that will keep the car from sliding off the track?