Homework Due

Read & Study 9.3-9.4, do #8-12 p. 133

Tonight’s HW

• Read & Study 9.5; do #13-15 • (3 points)

• Prepare for Open Notes Quest next class! • Use Web Quest• Use Study Guide

Do Now • Turn in HW• Take out your Stations POGIL from

last class• 10 minutes to complete all of your

Step 3’s (what ACTUALLY happened)

Homework Due

Read & Study 9.3-9.4, do #8-12 p. 133

Tonight’s HW

• Read & Study 9.5; do #13-15 • (3 points)

• Prepare for Open Notes Quest next class! • Use Web Quest• Use Study Guide

Do Now

3B

• Turn in HW• Take out your Stations POGIL from

last class• 10 minutes to complete all of your

Step 4’s (what ACTUALLY happened) and the SUMMARY #1-8

Centripetal Force• Means “center

seeking” or “towards the center”

• Any force that causes an object to follow a circular path.– EXAMPLE: The force that holds the

occupants in a rotating ride.

Centripetal Force• Name give to any force that

is directed at a right angle to the path of a moving object and that tends to produce circular motion

• If the centripetal force is removed, an object will follow a straight line, TANGENTIAL path (like in the plate & marble, and hula hoop demo!)

Centrifugal Force

• 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.

• Means “center fleeing,” or “away from the center”• The Physics F-WORD!!!! F is for fake, false, fabricated,

fictitious, forbidden, etc…• Very commonly misused. – (people say centrifugal when they should say centripetal)

• 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).

• Inward Force• Inward acceleration• Tangent velocity

Step 4’s *Complete!!!

They should all mention something about centripetal force: - If there is a centripetal force, it is

directed inward (so is the acceleration)

- That causes stuff to move in a circle- If you remove the centripetal force,

stuff no longer moves in a circle – it moves according to Newton’s 1st law

- The velocity is tangent SUMMARY - Complete #1-8

POGIL Review

• Turn to the summary portion at end of POGIL.

• 5 minutes to complete #1-8

• MAKE CORRECTIONS!!!!

1. The force that causes an object to move in a circular path acts…

A. B. C. D. E. F.

54%

31%

0%

8%8%

0%

A. Inward, towards the centerB. Curved, In a circleC. Tangent D. Curved, away from the

circleE. Outward, away from the

centerF. None of the above

2. If you were to remove that force from the object, the object would take a path that looked like

A. B. C. D. E. F.

0% 0% 0%0%0%0%

A. Inward, towards the centerB. Curved, In a circleC. Tangent D. Curved, away from the

circleE. Outward, away from the

centerF. None of the above

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?

A. B. C.

85%

0%

15%

A. RightB. LeftC. Neither

• Imagine that you are a passenger in a car which is making a left turn. – As the car begins to take the turn to the left, you

often feel as though you are sliding to the right. – The car is turning to the left due to the inward

CENTRIPETAL force, yet you feel as though you are being forced rightward or outward.

– In actuality, the car is beginning its turning motion (to the left) while you continue in a straight line path. This motion can be better understood by examining the animation below.

– http://www.mrwaynesclass.com/teacher/circular/CarAndCurve.htm

– http://www.physicsclassroom.com/mmedia/circmot/rht.cfm

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?)

A. B. C. D.

8%

58%

25%

8%

A. Gravity B. Support force C. Centrifugal force due to

friction D. Centripetal force due

to friction

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?

A. B. C.

15%

0%

85%

A. Outside seatB. Inside seatC. Doesn’t matter

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?

http://www.youtube.com/watch?v=DtNVLEXzcvM

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?

A. B. C. D. E. F.

8%

15%

0%

8%

0%

69%

A. Inward, towards the centerB. Curved, In a circleC. Tangent D. Curved, away from the

circleE. Outward, away from the

centerF. None of the above

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?

1. 2. 3. 4.

67%

8%

0%

25%

1. The water is being forced away from the clothes

2. The clothes are being forced away from the water

3. Neither the clothes nor water are being forced

4. Both the clothes and water are being forced

8. Explain why various race tracks have banked curves – or inclined walls.

http://www.youtube.com/watch?v=HmFMAGxGavY

1. 2. 3. 4.

75%

17%

8%0%

1. More centripetal force2. Less centripetal force3. More centrifugal force4. Less centrifugal force

Concept Development • On the back of your Study Guide • Complete #1 – 4! • We are going over this in 5 minutes!

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.

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.

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!

**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!

At this time… • Return your CLICKERS!• You have the rest of class to prep for your quest by

completing the…– Web Quest (not collecting or grading…but some of the

questions will be on your Quest)– Study Guide (not collecting or grading…but some of the

questions will be on your Quest)– Tonight’s HW (#13-15, 3 points)

• Next class we will…– Review HW #8-15– Take the quest– Start Ch. 12 (Big Bang, Black Holes, Universal Gravitation)