Rhett Allain
rallain
Posts by this author
April 14, 2010
Today is show and tell. I would like to show and tell you about two of my favorite textbooks for physics. Yes, I know. I have talked about these before, but you can't stop me. Both of these are alpha-super-awesome.
Matter and Interactions
This is a Calculus-based introductory physics textbook…
April 14, 2010
I was going through and tagging some old posts. While looking at a post attacking the movie Sunshine, I accidentally found something else on youtube.
Gravity in Sunshine
I could not find a clip online of the scene I want, so I made a cartoon. Basically, (oh - spoiler alert) some guys are trying…
April 13, 2010
Suppose I take a 1 kg ball and hold it near the surface of the Earth. What would be the gravitational force the Earth exerts on this ball?
And I could say "g" is:
The magnitude of this force would then be 9.8 Newtons. And, if I replaced the ball with a 10 kg ball, the force would be 98 Newtons…
April 12, 2010
This was a great question. When you come inside after playing in the sunny outside, why is it so dark?
Simple answer: because your eyes are smart. When you are outside, there is a lot of light. Really, it is too much light. To compensate for this, your pupils (the part of your eye that light…
April 12, 2010
I don't know.
One the one hand, it would seem that teachers (and really I am talking about grade school level and maybe middle school) need to be good an managing students. What should a teacher have to help students? I think the first big question is "what is going to happen in the classroom?"…
April 9, 2010
So, I complained about MythBuster's explanation of relative velocity. How would I explain this? I would start by saying that velocity is relative. Here is the definition for velocity:
I put the "avg" in there because it is more true. If the acceleration is zero, I could drop this. For the…
April 8, 2010
I have made some small changes to my physics textbook. Basically, I have been updating all my old posts so that you can find stuff. What I did was include tags for each topic. For instance, suppose you are looking at projectile motion. Well, I include a link to examples with projectile motion.…
April 8, 2010
In the last episode of MythBusters, they tried to reproduce the following experiment. Suppose you are driving in a car at 60 mph and you shoot a ball backwards at 60 mph (with respect to the car). Will the ball just drop (with respect to the ground)? Actually, it is a cool demo - I saw some…
April 7, 2010
I gave the following question on my last physical science (physical science for non-science majors) test:
Block A has a mass of 10 kg and volume of 100 cm3. Block B has a mass of 1 kg and a volume of 1 cm3. Which block has the greater density? Which block has the greater volume?
The results of…
April 7, 2010
Check out this video demo:
So, that is just plain water. If I am careful, I can make that thin aluminum disk stay on the surface of the water. This is not the same as floating in Archimedes principle. It is different. This is staying on the surface because of surface tension.
Bouyancy
I think…
April 2, 2010
The current push in our state is to improve college graduation rates. Who could argue that is a bad thing? Having more students succeed in college is a good thing. The problem is assessing the performance of the state universities by looking primarily at graduation rates. Why? Simply - if the…
April 2, 2010
In this part of the world, we have oak trees. Technically they are called live oaks - but I don't get it. Of course they are alive. I was at a soccer game and this is the tree I always look at.
Look how far those limbs extend horizontally. That branch is about 12 meters long. Why is this…
April 1, 2010
ZapperZ (at Physics and Physicists) recently had a post about Chad (from Uncertain Principles). It was sort of a review of Chad's book How to Teach Physics to Your Dog.
In this post, ZapperZ makes a very Feynman-like distinction between "teaching physics" and "teaching about physics". This is a…
March 30, 2010
This isn't much - really it is part of another post I am working on. The point of this post is to calculate the density of this piece of wood.
Really, there is a reason for this. I saw this little stick (sticklette?) and noticed that it was very cylindrically shaped. So, what if I just pretend…
March 29, 2010
Here is a quick Apolo Ohno quiz. Which one of these pictures is fake?
If you picked picture B - you are probably correct. That is a picture of "Apolo" being catapulted into a pool of slime at the Nickelodeon awards show (click on the link to see the video - I don't think I can embed it). Ok -…
March 26, 2010
I am surprised at how many people (chemistry faculty included) have never seen this demo. (oh, technically it is called a cartesian diver demo) Basically, you put some floating object that has an air space in a closed bottle of water. When you squeeze it, the diver goes down.
For my setup, I…
March 26, 2010
I am teaching physical science this semester. It appears that I will be teaching it again this summer. Ideally, I would like to switch to something like Physics and Everyday Thinking for large lecture courses. A course like this is being developed, but it isn't quite finished. Also, the current…
March 26, 2010
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,…
March 25, 2010
Think Thank Thunk is a relatively new blog from Shawn Cornally, a high school math and science teacher. I have found his posts to be quite entertaining. In Shawn's latest post, he talks about grades. You know I like to talk about grades. Shawn puts teacher into two groups in regards to their…
March 24, 2010
How does a suction cup work? It is all about the atmosphere. Here is a demo. Take some type of "suction cup" device. In this case, I used a toy dart. Stick it to something smooth and lift it up. Like this:
What lifts up the metal block? The atmosphere. Diagram time:
But this isn't a very…
March 23, 2010
I already looked at ESPN's Sport Science episode where they calculate that Marshawn Lynch produces 54,000 watts when pulling some tires. Yes, that is way too high. However, what would happen if some was actually that powerful? What could that person do? How fast could they run 100 meters? That…
March 23, 2010
I happened to catch two parts of two different episodes of Meteorite Men - a show about two guys that look for meteorites. In both of the snippets I saw, they were talking about a debris field for a meteor that breaks up. In these fields, the larger chunks of the meteorite are further down in the…
March 22, 2010
This is a topic that I am going to talk about in my physical science class. Might as well make a post about it, right?
Here is the deal. You are in a pool. You drop a quarter in the deep end and swim down to get it. I know the first thing you are going to ask: Why do I have a quarter in the…
March 19, 2010
Let me be clear. I am not really an attacker. If someone wrote a report about ski jumping or something and misused the word "momentum", no big deal. However, if you have a show that claims to be about SCIENCE and you are obviously putting a lot of money into this show AND a whole bunch of people…
March 16, 2010
Pre Reqs: vectors, forces
This is typically the first topic in the second semester of introductory physics - the interaction between objects with electric charge. There are 4 fundamental forces that physics typically looks at:
Gravity - an interaction between objects with mass - wow, I don't have…
March 16, 2010
The other day I was having a discussion with my brother about software and free software. Somehow I said I like it when software is free. Since he is a programmer and likes to get paid to program, he said "education should be free." I think I might agree with him.
I previously talked about…
March 14, 2010
Oh, I know you missed it. Really, it wasn't your fault. Pi day fell on a Sunday, so how are you supposed to have pi-day activities in class? Don't let it stop you. You are better than that. Do the activity anyway. What to do? Here are some suggestions. (Suggestions aimed mostly at the high…
March 13, 2010
Do you have an iPhone? I have an iPod Touch. Do you use vectors? Do you think RPN calculators are the bomb? Here is a RPN calculator for the iPhone that supports vector notation. VCalc by Silicon Prairie Ventures Inc. Oh - it is free. Here is a screen shot.
I played with it some, the only…
March 13, 2010
The most basic explanation of Pi is that it is the ratio of the circumference to the diameter for a circle. That seems simple enough, but it turns out that Pi is an irrational number - so you can't just write it down. Oh, I know that you are an uber-geek and you could recite the first 80 digits…
March 11, 2010
I already went over a Monte Carlo method for estimating Pi - you know, for Pi-Day (March 14). Well, here is a small addition. This is the same thing done in Scratch.
If you create an account on Scratch, you can download the code of any project. I like Scratch.