GT Rotation and Centripetal Day 11 Quarter 3 GT Rotation and Centripetal

Do you remember? Tangential vs. Rotational/Angular Get a clicker

You will look over and answer the next 3 questions as best you can for point A.

1. There is a centripetal acceleration at the top and it is pointed: a. Down b. Up 2. The AMOUNT of centripetal force you get by making a free body diagram and finding the amount of imbalance to the center. At A it would be: a. mg because mg is down b. T + mg because both forces are down c. mg – T because mg is down and T is up

3. If the string were to break at point A, at that moment the ball would go: a. Straight down because gravity is pulling it down at that point b. At a downish angle because it is pulled down by gravity but going left c. Straight left for that moment before it actually moves from gravity.

Now get your notes from last class, specifically the one with the record player

Above are 3 points on a disk. They are in a line (A, B, C) Above are 3 points on a disk. They are in a line (A, B, C). Notice here that they all go the same ANGLE in the same time, but they have different actual DISTANCES they cover in that time.

Try the next 5 questions for me, then we will vote on them. Use the record as reference, don’t be afraid to go back there and view it.

USING <, > or =, RANK THE ANGULAR VELOCITIES OF THE THREE POINTS. Angular velocity means how fast they are going in a circle every moment. Like the amount of degrees covered per second.

USING <, > or =, RANK THE LINEAR VELOCITIES OF THE THREE POINTS. Linear velocity is like circumference it goes per second.

Is there a point on the disk that has NO angular velocity? A) Yes! It must be the center, since it is not moving B) Yes! In fact, its every point, since they all go 360 degrees, so it cancels out. C) No! Even the center rotates, so all points rotate with some speed D) No! All the points have different angular velocities that are non-zero

Is there a point on the disk that has NO linear velocity? A) Yes! It must be the center, since it has no radius and thus no movement B) Yes! In fact, its every point, since they are not actually moving forward C) No! Even the center rotates, so all points move with some speed D) No! All the points have different linear velocities that are non-zero

What I expect you to be doing

Do points A B and C have a tangential acceleration Do points A B and C have a tangential acceleration? Do they have a centripetal acceleration. Assume its rotating like the record player DISCUSS AND JUSTIFY FOR 2 MINUTES

Check out the comic In other words, they have the same ROTATIONAL distance covered, but different TANGENTAL or LINEAR distances covered. So points on a record have different TANGENTAL speeds (meters/sec) but have the same ANGULAR speed (degrees per second)

TRY 6, 7, 8

6: When a wheel of radius R rotates about a fixed axis at a constant rate, which of the following statements are false? (more than 1 answer possible) A. All points on the wheel have the same angular speed. B. All points on the wheel have the same tangential speed. C. All points on the wheel have the same angular acceleration. D. All points on the wheel have the same tangential acceleration.

Don’t sent in, lets just see

Green Disk….get it out, remember Try the next 3 questions

9. GREEN DISK: What force kept the washers in place on the rough parts by resisting their desire to go forward? A. Gravitation B. Weight C. Normal Force D. Friction E. Tension F. Applied Force

10. GREEN DISK: Did the center washer have a tangential velocity 10. GREEN DISK: Did the center washer have a tangential velocity? An angular velocity? A. Yes to both! It had both angular motion and tangential motion since when stopped it would go in a straight line. B. No to both! It is not moving rotationally or linearly. C. Yes and No. It would move forward when disk is stopped, but is not rotating. D. No and Yes. It is rotating but would not go forward when stopped.

11. GREEN DISK: As you spin faster, does the force required to keep it curve go up/down? How can you tell? Not voting just trying to answer

Lets see it in action Describe it…

Lets see it in action “As they went in a circle, their arms supplied the force to keep them circling. At the fast speeds, their arms could not supply the force needed at that radius to keep them curved, so they flew off in a tangent line” Evaluate it, what is right/wrong here?

Lets see it in action “The idiot experienced more outward force than they could pull and flew out” Evaluate it, what is right/wrong here?

Try 12 and 13 12. You move a disk from the center towards the edge. As it goes closer to the edge, what happens to the angular velocity of it and the tangential velocity of it? Increase/Decrease/Not changing. Explain!

Try 12 and 13 13. Dario, a prep cook at an Italian restaurant, spins a salad spinner 20.0 times. The spinner has a radius of 5 cm. How many RADIANS did it go in those spins Call it Angular Distance Δθ, and how many METERS did it go (Called Regular Distance ΔX)?

15 A record that has a radius of 15 A record that has a radius of .15 meters starts at 20 radians per second and slows in 3 seconds to 5 radians per second. What is its angular acceleration?

15 A record that has a radius of 15 A record that has a radius of .15 meters starts at 20 radians per second and slows in 3 seconds to 5 radians per second. What is its angular displacement and tangential displacement at the center during that time?

15 A record that has a radius of 15 A record that has a radius of .15 meters starts at 20 radians per second and slows in 3 seconds to 5 radians per second. What is its angular displacement at the edge during that time?