Physics
rallain | December 29, 2008In part I of this post, I talked about the basics of projectile motion with no air resistance. Also in that post, I showed that (without air resistance) the angle to throw a ball for maximum range is 45 degrees. When throwing a football, there is some air resistance this means that 45 degree is not necessarily the angle for the greatest range. Well, can't I just do the same thing as before? It turns out that it is a significantly different problem when air resistance is added. Without air resistance, the acceleration was constant. Not so now, my friend.
The problem is that air…
rallain | December 26, 2008College football season is coming to an end (I guess technically, the season is over - it is bowl season). Anyway, this is something I wanted to do a long time ago, but I kept getting side tracked. If I don't do it now, I will never do it. Most people know that a ball without air resistance (traditional projectile motion) goes the farthest if you throw it at a 45 degree angle. What if there is air resistance? Why is 45 the best angle without air resistance? What other questions are there?
I posted about projectile motion before - so you might want to start there. When people say "…
rallain | December 23, 2008Clearly, I am not a professional blogger. I am an amateur. This is because I was under the impression that only amateur bloggers could compete in the blogging olympics. When did they change these rules? Anyway, Adam Weiner did a physics-based analysis of the latest Star Trek movie trailer. Here is the trailer:
In the trailer (oh, spoiler alert) a young Kirk jumps out of a car before it goes over a cliff. It does look odd, and that is why I had intended to analyze it. In Adam's analysis, at PopSci.com the basic approach was:
Take the initial velocity of the car (from the clip)
Assume…
rallain | December 22, 2008First, don't play with fire. Fire is dangerous. You can get hurt. Here is a video of two guys trying to (presumably) make the Miami Heat flaming basketball.
Note: the above is just a picture link to the actual movie. Embedding the movie was doing some weird stuff. In the movie, two guys pour gasoline on a basketball and then light it on fire. One of the guys then gives the ball a good kick. The result is that some of the flaming gas stays in place and some goes with the ball (and some gets on the guy's foot).
This could be a good example of the momentum principle (also know as Newton…
rallain | December 19, 2008I am sure I have mentioned the Discovery show Time Warp before. The basic idea of the show is to find how many cool things they can look at with an ultra slow motion video camera (btw - this is on my christmas list).
So, I have seen this Samurai guy on the show twice. Yes, he has a big sword. Yes, he could utterly destroy me if he wished. However, I can not handle him talking about physics. Mr. Samurai guy, please stop using the words "kinetic energy" until you know what they mean (I said please). Here is my first problem. Samurai guy is showing how to chop people down. He plans to…
drorzel | December 19, 2008When I saw ZapperZ's post about this paper (arxiv version, expensive journal version) from the group of Serge Haroche in Paris, I thought it might be something I would need to incorporate into Chapter 5 of the book-in-progress. Happily, it's much too technical to require extensive re-writing. Having taken the time to read it, though, I might as well make a ResearchBlogging post of it... (My comments will be based on the arxiv version, because it's freely downloadable.)
So, "Freezing Coherent Field Growth in a Cavity by the Quantum Zeno Effect." That's quite a mouthful. What does it really…
rallain | December 18, 2008I 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 really cool demo. Look at the first CD player that is on. When the guy taps it, it doesn't rotate but rather it wobbles. This is a rather difficult concept, but I am going to try to give a reasonable explanation.
I will start with angular momentum. Angular momentum is sort of like momentum (linear momentum…
rallain | December 16, 2008Wow. I wrote a post about Directly Down Wind Faster Than The Wind (DWFTTW) vehicles. At the time of this post, there are 37 comments for the original post. That is way more than I expected. This is very popular topic. Clearly, it brings a lot attention to Dot Physics. The first question - is this the kind of attention a naked person running through campus gets or is it a different kind of attention? I really don't mind either way.
I am going to try to look through all the posted material and see if I can add or subtract anything for the discussion.
First - the parameters of the…
rallain | December 15, 2008Maybe you have seen some of my posts on basic topics. One of the original ideas I had for creating the "basics" posts was so that I would not need to keep repeatedly explaining what the fundamental physics concepts were for each post. I can only explain the work-energy principle so many times before I go crazy (maybe I am already there).
So anyway, it appears I have written enough of these posts that they could somewhat be considered a textbook. I have thought about textbooks for some time now. I considered writing one, but wasn't sure where to start. This way was really nice because I…
rallain | December 12, 2008Pre Reqs: momentum principle, forces,energy, vectors
Really, there is not much new here. This is an introduction to objects that interact. To describe this, I will need to pull several different ideas together (that you have probably already looked at). Let me start with a simple case. Suppose I have two objects, maybe they are two asteroids in space. I will call them asteroid A and B:
In this situation, the two objects have different momentums but one interaction between them. Notice that the gravitational force on asteroid A is the same magnitude but opposite direction as the force…
drorzel | December 12, 2008I subscribe to Scientific American, but I'm usually several weeks behind on reading it, so it was only Thursday that I noticed this surprising article about particles bouncing back from attractive forces:
This effect is the converse of the well-known (if no less astounding) phenomenon of quantum tunneling. If you kick a soccer ball up a hill too slowly, it will come back down. But if you kick a quantum particle up a hill at the same speed, it can make it up and over. The particle will have "tunneled" across (although no actual tunnel is involved). This process explains how particles can…
pontiff | December 11, 2008Well I'm sure the physics blogosphere is abuzz with the news that Steven Chu is expected to be named by President-elect Obama to head the Department of Energy. Wait let me look. Yep: heisendad, varyingsean, chunothsu, angryphysicist, nanodude, lubotic, toinfinityandbeyond and thedeterminantsnotzero. (OK that last comes from non-physicists, but I couldn't resist a linear algebra joke.)
Since I have little to add besides the fact that laser cooling rocks, I present the first few lines of a song that was sung by a band at Berkeley concerning the person Chu shared the Nobel prize with, Cohen-…
rallain | December 10, 2008A commenter (Joe) suggested I look at vehicles powered by the wind that can move faster than the wind. This also came up on Swans on Tea. One of Joe's points was that I should do this BEFORE MythBuster's gets to it. And so I shall. I know this is one of those topics that can never really be won - like "the moon landings were fake" or "you can run your car on water". I will try anyway. If you are not sure what this "faster than wind" thing is all about, check the Swans on Tea link or this boing boing link.
There has been a ton of stuff posted about DWFTTW vehicles. Literally a ton. If…
drorzel | December 10, 2008I'm a little cranky after a day of reviewing grant proposals, so it's possible that I'm overreacting. But commenter Neil B has been banging on about quantum measurement for weeks, including not one, not two, but three lengthy comments in Tuesday's dog post.
For that reason, I am declaring this post's comments section to be the Official Neil B. Quantum Measurement Thread. Until such time as I declare the subject open again, this is the only thread in which I want to see comments about quantum measurement. Attempts to bring the subject up in comments to other posts-- even other posts having to…
drorzel | December 9, 2008I'm sitting at the dining room table eating lunch, when I get the feeling of being watched. I look around, and see the dog across the room, curled up on her pillows staring at me. She's quietly chanting to herself "I get stuff. I get stuff. I get stuff."
"You're not trying that hypnosis thing again, are you?" I ask. "You know it won't work."
"No. I'm manipulating the wavefunction of the universe to bring me good things. Such as, for example, that cheeseburger you're eating."
"Really. Manipulating the wavefunction of the universe?"
"Really. You see, all conscious beings are surrounded by an…
rallain | December 9, 2008VPython 5.0 is mostly out (in release candidate). To tell you the truth, I have been holding off on some vpython programs because I wanted to do them in the NEW vpython, not the OLD vpython. So, if you want to get the new vpython, go to http://vpython.org/index5.html. What is so great about VPython 5.0? Here a couple of things:
Runs in Mac OS X without X11. Maybe this isn't that big of a deal, but it makes me happy. If you don't use OS X, I guess this doesn't matter.
Textures. You can map textures and images onto objects. This won't really help with the calculations, but it will…
drorzel | December 8, 2008I made a run to the library last week on one of the days I was home with SteelyKid, as an excuse to get out of the house for a little while. I picked up three books: Counterknowledge, The Devil's Eye by Jack McDevitt (an Antiquities Dealers Innnnn Spaaaaaace novel, and a good example of Competence Fiction), and a pop-science book titled The Age of Entanglement: When Quantum Physics Came of Age by Louisa Gilder, because it looked fairly relevant to my own book-in-progress.
Amusingly, my RSS feeds yesterday brought me the latest in a series of posts in which ZapperZ waxes peevish about the book…
drorzel | December 7, 2008I spent most of yesterday helping out with an on-campus workshop for high school teachers and students. Seven high school physics teachers and seventeen high school students spent the day doing a half-dozen experiments to measure various physical constants.
I was in charge of having them measure Plack's constant using the photoelectric effect. The actual measurement (made using a PASCO apparatus) takes about fifteen minutes, so I gave each group a quick explanation of the history: Einstein proposed the particle model of light as an explanation for the photoelectric effect in 1905, and nobody…
rallain | December 6, 2008This comes from Buzz Out Loud Episode 865 which got the story from Slashdot regarding a possible new technology that would use piezoelectric devices to charge cell phones while you talk. The original article the slashdot story pointed to talked mostly about the advances in piezoelectric devices, but I want to look at the possibility that sound could charge a phone.
First for the basic physics. How do you make sound and what is it? Sound is a compression wave in the air. To make a sound you need something to push the air (yes, I simplified this quite a bit). When that something pushes the…
rallain | December 5, 2008Let me start off by saying I think I first read about this on HowStuffWorks.com (many years ago). So, why are christmas lights so cool? They are cool because they are a whole bunch of lights in series, but they still work if one of the bulbs gets burnt out. If you are not familiar with circuits, a series circuit is one in which all of the current goes through all of the items in that circuit (as compared to the case where the current gets split up). Here is an example of a series circuit with two bulbs.
In this case, the current comes out of the battery, goes through one filament and…