# Could cars slow down the Earth?

Time for another Fermi problem. There was a recent story in Science News that talked about the effects of the Chilean quakes on the Earth’s rotation. The basic idea is that some ginmourmous amounts of rock moved closer to the Earth’s center. Since the angular momentum of the Earth is conserved, the angular rotation rate…

# Angular Momentum Example

I showed this demo in class and I was surprised at how cool the students thought it was. They actually thought it was some kind of trick. It is not a trick. Instead, this is an example of the angular momentum principle. If you want to try this yourself, I guess you are going to…

# Playing with a merry go round

Thanks to reader Cleon for notifying me of this video on youtube. Check it out. First, some notes. I am sure you noticed that the aspect ratio is incorrect (at least that was the first thing I noticed). The boys must have made a 16:9 video, but then uploaded it to youtube as a 4:3.…

# Flywheel in a bike. What is up with the gyrobike?

My friend J sent me a link to this gyrobike (http://www.thegyrobike.com/index.php). From what I can tell, it’s a flywheel that you put in the front wheel of a bike. The site claims that this will help kids learn how to ride a bike. So, what do I think? Clearly, this is a real product, but…

# Rotational Energy of the Earth as an energy source

Note: This is an old post from the time before my blog was in wordpress. I noticed there was some incoming link for this, and I never moved it over. Here it is in it’s unaltered (except for this part) format. I don’t know why I even suggest a new energy source. Fusion power is…

# Moment of Inertia Demo

When I was talking about balancing a stick, I mentioned the moment of inertia. Moment of inertia is different than mass, but I like to call it the “rotational mass”. What does mass do? Things with larger mass are more difficult to change their motion (translational motion). A similar thing is true for the “rotational…

# CD Players in space and rotations of a rigid body

I saw this video on several places. It shows an astronaut playing with a CD player. I wish I were an astronaut. I would probably not stop throwing up though. It would still be worth it. You can only throw up so much right? (I know the answer to this question). Anyway, this is a…