I am missing… • 2 1 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.

Homework Due

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

Tonight’s HW

Read & Study 9.5; do #13-15

Prepare for Open Notes Quest 2 classes from now (Extra Credit due that day, too!)

Do Now Take a Ladybug Do Now & Clicker from my desk – 5 minutes to complete! May work with others but stay in FRONT portion of room, not lab benches. Channel 41 Channel

Use this as a hint…

• http://phet.colorado.edu/en/simulation/ladybug-motion-2d

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

A. B. C. D.

0% 0%0%0%

A. B. C. D.

Do Now Answers #1. The ladybug moves CLOCKWISE. What

could the FORCE and VELOCITY vectors, respectively, look like? (A, B, C, or D)

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

A. B. C. D.

0% 0%0%0%

A. B. C. D.

Do Now Answers #2. The ladybug moves CLOCKWISE. What

could the ACCELERATION and VELOCITY vectors, respectively, look like? (A, B, C, or D)

Do Now Answers #3. The ladybug moves COUNTERCLOCKWISE.

Draw and Label the FORCE, ACCELERATION, and VELOCITY vectors.

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

A. B. C. D. E.

0% 0% 0%0%0%

A. B. C. D. E.

Do Now Answers #4. Imagine the bugs are attached to a bar as

shown.

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)

Stations • Please continue to work on the POGIL from last class.Remember:Goggles at the water bottle station – NO EXCEPTIONS!!!1. Borrow lab materials for a station. 2. Complete Demo.3. Return lab materials4. Fill in STEP 3 & STEP 4 boxes on your POGIL5. Check in answers with teacher.6. 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.

POGIL Review

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

Channel!

1. The force that causes an object to move in a circular path acts (see board for diagram):

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

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

A. B. C. D. E. F. None of the above

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

like (see board for diagram):

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

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

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

0% 0%0%

A. RightB. LeftC. Neither

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.

0% 0%0%0%

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.

0% 0%0%

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

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):

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

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

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

0% 0%0%0%

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.

1 2 3 4

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

Concept Development

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

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…

• 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!

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.

Three locations on our Earth are shown. Which has the

GREATEST ROTATIONAL SPEED?

1 2 3 4

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1. A2. B3. C4. All have the same

rotational speed

Three locations on our Earth are shown. Which has the

GREATEST TANGENTIAL SPEED?

1 2 3 4

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1. A2. B3. C4. All have the same

tangential speed

Chapter 9: Circular Motion

Axis• An axis is the straight line around which

rotation takes place

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.

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

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.

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!)

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

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.

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.

• 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).

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

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

YesYes