Dot Physics

Archives for January, 2009

Physics of the Water Rocket

I said I would come back to this, and I am. I am a man of my word. Yesterday, I posted a link to a video of this really cool water rocket thingy. How does this work? What is the physics going on here? I think this can be best explained with the momentum principle.

Buzz Out Loud and Black Holes

Buzz Out Loud is one of my favorite tech podcasts. Unfortunately, I am a little behind in the episodes. However, in the episode 900 there was an email from a listener regarding LHC and black holes. The emailer claims that a massive black hole would mess up Earth’s orbit. This is not quite true. I…

I saw this on Hack a Day, but I am sure it has been posted in other places also (seems like something that would be on Swans on Tea). Check it out. Amazing New Water-Powered Jet Pack – Watch more free videos Some pretty cool stuff. I am pondering the questions to be answered right…

I really didn’t want to post this, but I am going to anyway. I used ScreenToaster.com to make a screen capture movie (with audio) of a tutorial on spreadsheets. This should accompany my previous post on numerical calculations. Free online screen recorder

Kobe Bryant Jumping Over a Car

We have all seen the Kobe Bryant video of him jumping over an Aston Martin – this keeps coming up on the Internet. There has been vast discussions of whether this is real or fake. I will do my best to examine the evidence. In short (in case you don’t want to read the whole…

Grades: curve or no curve

Should you grade on a curve or not? If you are student, the answer is clear: go by whatever the instructor does. Otherwise, you have a choice. I don’t like to tell other instructors or faculty what to do because I respect their freedom. For my classes, there is no curve. Why? Well, the question…

Modeling the head of a beer

When you pour a beer, there is this foamy top called the head. The size of the head decreases over time. What is this process dependent on? Clearly, little bubbles of beer are popping. Does each bubble have an equal probability of popping? Do only the bubbles on the top (or bottom) pop? I became…

When is the Sun directly overhead?

Question: When is the Sun directly overhead? (assume you are in the United States of America) Common Answers: Everyday at noon. On the summer solstice (June 21ish) Answer: For continental U.S. the answer is never. Since the Earth’s rotation axis is tilted 23.5 degrees with respect to its orbital motion around the Sun, one would…

Unit conversions for mere mortals

So, you are taking a college science course. Maybe it is physics, maybe it is chemistry, maybe its a lab. Either way, you always end up with these problems that involve unit conversions. You think you have the hang of it, but sometimes you make some mistakes. Here is my explanation for converting units. Convert…

90,000 KWhr for half a month

I just can’t pass this up. One of the chemistry majors had a complaint with the power company. After an unusually high previous power bill, they checked the electric meter half way through the month. The meter said they had used 90,000 kilowatt-hrs of electricity. That is a lot of energy. It is also a…