Conserving Angular Momentum, when Sum of the Torque = zero
- Angular momentum = I*alpha, kind of like linear momentum = m*v
- Torque SOMETIMES = I * alpha, as stated above in rotational dynamics. Torque ALWAYS = rate of change of angular momentum
- For instance if Torque = zero, then angular momentum is conserved (just like we conserve momentum if there’s no outside force) it doesn’t mean that alpha = zero, like acceleration = 0 if the sum of the forces = 0, Think of the spinning skater pulling in her arms, yielding a positive angular acceleration.
- Collect PS #7,
- PS#8 is posted please read through it.
- Read 10.5 in your text and check out example 10.14
- Please watch this video on torque = time derivative of angular momentum
- Please see video on Coriolis Effect , made by students from Fall, 2014
- PS#9 due next week has been posted. Please take a look at it.
- I posted my summary and reflection from your week 8 feedback on the main webpage
How can a point mass (with no radius and no moment of inertia) have angular momentum? It all depends on the impact parameter!!
- Angular Momentum of a Point Mass
- Bullet Hits Block Veritassium
- Please read through PS#8
- Solutions to MT#2 posted on main website. Please make sure as soon as possible that you would get all these problems correct if you were to encounter them again.
Day 3: More on how Torque = rate of change of angular momentum
- Please see the video on angular momentum: Wheel Kick and Figure Skating
- Veritassium Which Block Goes Higher?
- Big Exam #6 – Solutions posted on main class page
Torque is rate of change of angular momentum so dL = (torque)*dt. However, angular momentum is a vector, so you also need torque to change the direction of angular momentum.
- Please see Precession by Veritassium
- read 10.8 in your text about precession.
- Optional: I made this video on precession. It’s long and slow, but it has 2700 views, so some people find it helpful: Pete’s Precession Video
- Rotational Big Picture
- Explanation of Veritassium Bullet Problem
- See solutions for BE#7
- Angular momentum and Gyroscopic stability. We have some cool demos for this.
- Why must we spin frisbees or footballs to make them fly stable? What is counter steering on a motorcycle?
- How is this related to precession?
Friday. You have until midnight tonight to post your link on the website for full credit.