1. Warm-Up! Tuesday, January 29
In your notebooks, answer the following two (2) questions according to section 11.7 in your text (starting on Page 163).
1. If an ice skater who is spinning pulls her arms in so as to reduce her rotational inertia to half, by how much will her rate of spin increase?
2. What happens to a gymnast's angular momentum when he changes his body configuration during a somersault?
What happens to his rotational speed?

2. Pass back and go over Review Questions # 1-10, pg. 147
3 points possible - to get full credit you must have written out both questions and answers.
Accompanying diagrams were also a bonus.
Answers:
1. It has more mass toward the thicker end.
2. CG
3. Follows parabolic path
4. When gravity doesn't vary over the object; when gravity does vary
5. The planetary system displaces CG from the center of the star.

3. RQ #6-10, pg. 147
6. Suspend it from two or more points and see where the lines of suspension intersect.
7. Donut, boomerang, hollow ball, examples continue... What are some other examples?
8. Its CG is above a support base.
9. Until the CG extends beyond the support base
10. Both need almost constant readjustment.

4. Physics challenge: males vs. females
Look at the top of page 141.
Who was able to pick up the chair after resting their head against the wall?
Look at the last paragraph on page 145.
Why can't you touch your toes when pressed up against the wall?
Explain the situations scientifically.
Did you notice any patterns? Why do you think?
You were to list group members, observations, diagrams, explanations, etc.

5. A few more examples of "displaced CG":
1. Attempt to stand up without putting your feet under the chair.
Why won't it work?
2. Stand facing a wall with your toes touching the wall. Now try standing for a few seconds on your tippy toes unaided.
Why will it not work?
How could you get it to work?

6. See page 142 in your text and explain the difference between:
unstable, stable, and neutral equilibrium.
Unstable - if object is displaced, CG falls
Stable - displacement causes CG to rise
Neutral - CG neither rises nor falls when object is displaced.
Gravitational potential energy of the object is more when the CG of an object is raised.

7. Moving on to Chapter 11 - Rotational Mechanics
What is the difference between The Conservation of Angular Momentum (Ch. 11) and The Conservation of Linear Momentum (Ch. 7), other than the fact that one is a straight path and one is in a circular path?
How is it conserved in both cases?
What are the similarities?
You could create a chart with similarities on one side, and differences on the other.

8. Both are "inertia in motion": products of mass multiplied by velocity (more mass and/or more velocity equal more momentum).
Both are vector quantities.
Both exhibit Newton's 1st Law of Motion: resistance to changes in motion.
Angular momentum has to factor in radial distance (distance of rotating mass from the axis)
To say that it is "conserved" is to say that the energy doesn't change (or "disappear") after some event.
What are some other real-world examples?

9. Answers to today's warm-up questions:
See page 163.
1. Her rate of spin will double if she pulls her arms in so as to reduce her rotational inertia to half.
2. Angular momentum of the gymnast does not change; angular speed changes.

10. Angular Momentum video clips:
See the blog posting for Friday, January 25.

11. For the rest of the class period:
Be sure to complete and turn in the two (2) worksheets from last Friday
covering Chapter 11 - Rotational Mechanics.
Staple them together in numerical order and turn in to the basket.

12. Video Activity:
We will now begin to watch one of the most popular science television shows ever.
Complete the video response sheet as you go view the program, turn it in at the end of class.
Cosmos, by Carl Sagan 0