I am missing…

1. I am missing… • 21 classroom textbook (1 was returned) • 2 bottles of white out • 1 calculator Until these items are returned, borrowing privileges are suspended… bring your own textbooks and your own calculators.

3. Use this as a hint… • http://phet.colorado.edu/en/simulation/ladybug-motion-2d

4. #1. The ladybug moves CLOCKWISE. What could the FORCE and VELOCITY vectors, respectively, look like?

5. Do Now Answers #1. The ladybug moves CLOCKWISE. What could the FORCE and VELOCITY vectors, respectively, look like? (A, B, C, or D) Velocity is a straight line TANGENT to the circle Force is directed INWARD at a right angle to velocity Answer is C

6. #2. The ladybug moves CLOCKWISE. What could the ACCELERATION and VELOCITY vectors, respectively, look like?

7. Do Now Answers #2. The ladybug moves CLOCKWISE. What could the ACCELERATION and VELOCITY vectors, respectively, look like? (A, B, C, or D) Velocity is a straight line TANGENT to the circle Acceleration is directed INWARD at a right angle to velocity Answer is C

8. Do Now Answers #3. The ladybug moves COUNTERCLOCKWISE. Draw and Label the FORCE, ACCELERATION, and VELOCITY vectors. Velocity is a straight line TANGENT to the circle Acceleration & Force Are both directed INWARD at a right angle to velocity

9. #4. Imagine the bugs are attached to a bar as shown.

10. Do Now Answers #4. Imagine the bugs are attached to a bar as shown. Bug X has a larger tangential speed; Bug Y has a smaller tangential speed; Answer must be B!

11. Do Now Answers #5. On Figure 3, Draw your own set of acceleration vectors for the bugs at points X & Y. (You may want to use pencil if you think you’ll need to erase when we correct) Both bugs must have INWARD directed forces, And therefore inward directed accelerations!

12. Stations • Please continue to work on the POGIL from last class. Remember: Goggles at the water bottle station – NO EXCEPTIONS!!! • Borrow lab materials for a station. • Complete Demo. • Return lab materials • Fill in STEP 3 & STEP 4 boxes on your POGIL • Check in answers with teacher. • Repeat until finished. While this is going on, teacher will be calling you up individually to discuss exit slip from last class. After completing this, we will review the Concept Development page you complete for HW a few nights ago. If there is time, we will popcorn all HW. If not, we will do that before your Quest.

13. POGIL Review • Turn to the summary portion at end of POGIL. • We will we clicking in as a class  Channel 41 Channel!

14. 1. The force that causes an object to move in a circular path acts (see board for diagram): • None of the above

15. 2. If you were to remove that force from the object, the object would take a path that looked like (see board for diagram): • None of the above

16. 3. You are traveling in the passenger seat of a car. All of the sudden, the driver makes a sharp LEFT turn. Do you feel as if you are moving to the right, or the left? • Right • Left • Neither

17. 4. When a car travels in a circular path, what force holds the car in the curved path? (Hint: Is it easy to maneuver a car when road conditions are icy?) • Gravity • Support force • Centrifugal force due to friction • Centripetal force due to friction

18. 5. Please answer the following question: When riding the “Himalaya” or “Music Express” carnival rides, is it more comfortable to sit on the outside seat or the seat closer to the center? Why? • Outside seat • Inside seat • Doesn’t matter

19. 6. Suppose you were to let go of the string holding the water bottle. (DO NOT DO THIS) What path would the water bottle follow? (see board for diagram): • None of the above

20. 7. Picture a washing machine drum. It rotates, and has holes in the side of the drum. Is the water being forced away from the clothes, or are the clothes being forced away from the water? • The water is being forced away from the clothes • The clothes are being forced away from the water • Neither the clothes nor water are being forced • Both the clothes and water are being forced

21. 8. Explain why various race tracks have banked curves – or inclined walls. • More centripetal force • Less centripetal force • More centrifugal force • Less centrifugal force

22. Concept Development • You have a few minutes to review with peers, then we are popcorning to go over!

23. Remember – YOU want to move according to Newton’s 1st Law – no change in motion. Only a FORCE will change your motion. Remove the force (in this case, back of seat), you tend to stay at rest.

24. Remember – YOU want to move according to Newton’s 1st Law – no change in motion. Only a FORCE will change your motion. Remove the force (in this case, seatbelt), you tend to keep a constant velocity.

25. Remember – YOU want to move according to Newton’s 1st Law – Straight line, same speed. Only a FORCE will change your motion. Remove the force (in this case, seatbelt and car door), you tend to keep a constant, TANGENT velocity – you would fly out of the car by virtue of your inertia, since there would be NO force on you!

26. **Summary** • CENTRIPETAL force is always inward, towards the center of the circle. (So is the acceleration! Object is changing direction, so its velocity is changing, so it is accelerating INWARD just like the force!) • CENTRIPETAL force causes objects to MOVE in a circular path • CENTRIFUGAL is the FEELING of being thrown outward (due to INERTIA / 1st Law), but it is not a real force! There is NEVER a force that throws you “outward” • When you turn, CENTRIPETAL force keeps you turning. Remove the force, you move in a tangent path because there is NO FORCE acting on you – you move by virtue of your own inertia / Newton’s 1st Law!

27. At this time… • Please continue to check your Ch. 9 Packets by borrowing a key, checking, and correcting. • REMEMBER - The answer means NOTHING if you are unsure how to GET to the answer! If you need help / clarification / etc., ask a peer or a teacher! • If you finish…please go back and review all book HW up to this point. CORRECT your answers by discussing with your peers and reflecting on what you have learned in class. • We are exiting with a clicker review!

28. Exit • Click in your answers. • Jot down notes if you want. • Before you leave, return your clickers • You can download this PowerPoint – there are more slides summarizing the Chapter included – we just did not look at them during class! Feel free to download, review, print, etc.

29. Three locations on our Earth are shown. Which has the GREATEST ROTATIONAL SPEED? • A • B • C • All have the same rotational speed

30. Three locations on our Earth are shown. Which has the GREATEST TANGENTIAL SPEED? • A • B • C • All have the same tangential speed

31. Chapter 9: Circular Motion

32. Axis • An axis is the straight line around which rotation takes place

33. Rotation • When an object turns about an internal axis. • An axis located within the body of the object • The motion is also called spin. • Earth Rotates about its axis once every 24 hours.

34. Revolution • When an object turns about an external axis. • Earth Revolves around the sun once every 365¼ days.

35. Linear Speed • What we simply called speed in Chapter 2. • A distance moved per unit time. • Linear speed varies based on radius of a circle. • On the Merry-Go-Round, the horses on the outermost ring have to travel faster to keep up with the horses that are closer to the center axis.

36. Tangential Speed • The speed of something moving along a circular path. • We call it tangential motion because the speed is always tangent to the circle. • We can use tangential speed and linear speed as the same thing for circular motion. (SYNONYMS!)

37. Rotational Speed • The number of rotations per unit of time. Symbol (ω-omega) • Sometimes called angular speed. (synonyms!) • All parts of the merry-go-round rotate about their axis in the same amount of time. • Measured in RPM (rotations per minute) • The record player rotates with a rotational speed of 72,000RPM. • Tangential Speed = Radial distance x rotational Speed • v = r ω

38. Centripetal Force • Any force that causes an object to follow a circular path. • Centripetal means “center seeking” or “toward the center.” • The force that holds the occupants in a rotating ride.

39. Centrifugal Force • The Physics curse word!!! • The forbidden F word – fake, false, fictitious, • Very commonly misused. • Means “center-fleeing” or “away from the center.” • It is NOT real force because it is NOT part of an action-reaction pair! • Misconception that centrifugal force pulls you outward during circular motion. THERE IS NO FORCE PULLING YOU OUTWARD! • Actually, it is just the inertia of the body traveling tangent to the circle.

40. As a ball is whirled above the head, it is the inertia of the ball that wants to continue moving in a straight line. Instead, the ball is forced inward to change its direction (Centripetal Force-supplied by string).

41. In Summary… • Newton’s 1st Law states that UNLESS there is a net force, • an object at rest will stay at rest • An object in motion will stay in motion without acceleration • In other words, it will not accelerate  it will not change its velocity  it will not speed up, slow down, or change direction. • Does the marble travel in a straight line? • So…does it change direction? • So… does it accelerate? No Yes Yes

42. In Summary… • Newton’s 2nd Law states that IF there is a net force, • an object will accelerate • In other words it will change its velocity  it will speed up, slow down, change direction or any combination of the 3. • Does the marble travel in a straight line? • So…does it change direction? • So… does it accelerate? • So… is there a force that causes this acceleration? Your goal is to figure out what direction this force acts (and therefore, what direction the acceleration acts, since the acceleration is in the same direction as the net force) No Yes Yes Yes