rallain | April 14, 2010Today 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 (from Wiley). The intended audience are engineers and scientists - in particular physics majors and chemistry majors. Computer science majors would do well to use this book also. So, why do I like this? Here are some of my favorite features.
"Modern" and fundamental approach. If you look at…
rallain | April 14, 2010I 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 to get from one spaceship to another by shooting out of the airlock and into the other. They fly through space and into the other airlock, close the door and emergency pump the air in. When the closed air lock fills with air, they all fall down. Since there was no online video version, I made a…
rallain | April 13, 2010Suppose 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. What does this have to do with the electric field? Well, you are probably already familiar with this idea of the gravitational force. Guess what? "g" is the gravitational field. Basically, it is the force per unit mass due to the Earth. This is only approximately constant. If I get very far…
rallain | April 12, 2010This 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 goes through) closes some. And then, when you go back inside your pupils are still small. Inside (even with the lights on) is not nearly as bright as outside. Not enough light is getting through your pupils and so everything looks "dark".
Here is a simple demo. While inside, take a flashlight (not…
rallain | April 12, 2010I 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?" Let me take two extremes:
Lecture-traditional. Basically just your normal lecture.
Something else - for example stuff that high school physics/math/computer science teacher Shawn does.
Although I really don't know the answer, I am going to lean towards - teachers need some content expertise.…
rallain | April 9, 2010So, 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 rest of this post, I am going to assume zero acceleration. Ok. But what is the r vector? It is simply a vector from the origin to the object. Here is a picture.
Simple, right? And so the velocity tells how this vector r changes. But wait. Who says that I used the correct origin? How do you…
rallain | April 8, 2010I 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.
Some of the examples may not be the best for that topic, but it is better than nothing. Really, what I need to do (other than finish tagging all my old posts) is to pick one good example for each topic. There is always tomorrow.
rallain | April 8, 2010In 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 Japanese show did this a while ago.
So, what is the problem? The problem is with the MythBusters' use of their terms to explain this thing. Let me look at a couple of the things they said to explain this (surprisingly, they described it several different ways). This first one is my favorite.
Bad…
rallain | April 7, 2010I 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 this question are interesting. Of the respondents, 33 answered both parts in a meaningful way. 8 of these 33 answered that the one with the greatest density had the greatest volume (that is 24%). Most of these 24% said that 1 cm3 was greater than 100 cm3. However, there were some that said the…
rallain | April 7, 2010Check 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 my best explanation of buoyancy was in the post about MythBusters floating a lead balloon. But, basically for buoyancy there is an upward force from the water on the thing that is floating. If I want to explain this in terms of the particle model of a gas or fluid, I could say that the particles in…
rallain | April 2, 2010The 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 goal is to just raise graduation rates, that is easy to do. Just make sure more students pass. Is this really what we want? I think not.
Louisiana Governor Ricky Bobby Jindal compared the poor graduation rates of the state universities to a football coach without a winning season hinting that you…
rallain | April 2, 2010In 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 amazing? Have you ever tried to hold an 8 foot 2 x 4 board horizontally by holding one end? Pretty tough. How about I calculate the forces needed to hold that branch in place? I will do a simple model and then maybe later I can make it more complicated. Suppose I replace that limb with one straight…
rallain | April 1, 2010ZapperZ (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 really good point - that to learn physics you have to do physics. I completely agree. It is just like riding a bike - you have to ride a bike to learn to ride a bike.
So here is the question. What do I do here on this blog? I don't know. Do I talk about physics? Yes? I do not teach physics -…
rallain | March 30, 2010This 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 it is a cylinder to calculate the volume? This way I won't have to get it wet or anything (because I might need this stick later).
First the mass
Yes, there is some uncertainty in the mass - but it is small. I put the stick on balance and I will use a value of m = 28.9 g or 0.0289 kg.
Volume
The…
rallain | March 29, 2010Here 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 - time to crank out an analysis.
I think I could approach this analysis from a couple of directions. Since all I have is a crappy version of the video, I could just look at "could this be possible"? The other analysis I could do would be to measure his acceleration in free fall. Let me start with…
rallain | March 26, 2010I 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 used a glass eye-dropper. Put it in a cup to make sure it just barely floats and then put it in a completely full water bottle. If you don't have a eye-dropper, you can use anything that floats with an air space. I have done this with part of a straw before. Fold a small section of a straw in half…
rallain | March 26, 2010I 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 version includes chemistry and physics. I really need something different (we offer physical science 101 is physics and 102 is chemistry).
The current course is pretty traditional. Your basic physical science stuff. It has the following content.
Forces and Motion
Newton's Laws
Projectile motion…
rallain | March 26, 2010Time 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 would increase. The estimated change of the day was by about 1.26 microseconds.
Could all the cars in the USA be used to change the rotation of the Earth?
Well, I shouldn't have phrased the question that way. Of course 1 car technically is all you need to change the…
rallain | March 25, 2010Think 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 ideas about grades:
"
Grades should reflect a student's progress with course material. Where an A+ indicates mastery.
Grades should be an amalgam of student's knowledge, behavior, and anything else the teacher wants to control.
"
I was in the middle of posting a comment to this post, but it was…
rallain | March 24, 2010How 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 realistic diagram. Actually, the suction cup would be pushing down on the block because the force from the atmosphere would be too large to balance with the weight. Let me put some numbers in here. Suppose this is an aluminum block - I just going to pretend it is 4cm on a side (and a cube). In…