rallain | January 8, 2009I am going to tell a story and then calculate the probability of part of it happening. Really, it's just an excuse for me to put this online (since no one got hurt).
My parents have this house on a lake, but it is really hilly. There is a dock down there, but it is like a bajillion stairs to get there. Good for exercise, bad for carrying a cooler full of beer (and ice). I don't know where he found about it, but my Dad got these guys from Minnesota to install this tram thingy. Basically it's a little train car with benches that rides down on two rails to the dock below. The thing is…
rallain | January 7, 2009I saw this video posted on Physics and Physicists:
It reminded me that I had at one point tried to analyze this. I had actually posted something about this on the first generation of my blog (which no longer exists). I have found the analysis, and here it is from the archives. Thanks ZZ for reminding me.
Could this be true, or is it fake? I started to do an analysis of the trajectory, but I found the following frames:
Look at the guy's back. His back starts moving before the water bottle rockets. It must be some type of cable pulling him. If the rockets were propelling him, the rockets…
rallain | January 6, 2009The Teaching Professor has a short note about students cramming for exams. The article talks about how you should deal with students cramming for exams. It includes the correct answer: you shouldn't do anything accept maybe change your tests.
What is the purpose of a test? It is some way to evaluate what a student has mastered. If a student can "master" something by spending a couple of hours right before the exam, is it really worth mastering? The real problem is that many tests seem to focus on recall type information. These are (in my humble opinion) mostly pointless. What does it…
rallain | January 5, 2009I finally saw the movie WALL-E. Good flick, I liked it. There was, however, one part I must comment on. You know I can't help myself. I feel like the shark Bruce in Finding Nemo. I try not to attack, but there is a tiny drop of blood in the water. Here is the scene that I want to talk about:
I guess I should give a spoiler alert. Although, I will not talk about the plot of the movie.
In this scene, WALL-E is hitching a ride on this space craft. The space craft is entering a hanger deck of a space station. While the hanger door is still open, WALL-E is clearly hanging on so that he…
rallain | January 3, 2009I finally saw the movie Iron Man. It was good. I feel that I am qualified to evaluate the movie. When I was in high school, I was totally into comic books. Mostly Spider-man, but I still have a significant collection of Iron Man comics. Ok, now you know I am not an Iron Man attacker. I will now attack the movie. Sorry, it's what I do (remember, I already said I liked it). There are several things I could comment on, in fact I recall some other blog talking about the physics of Iron Man.
My attack will center on the scene where Tony Stark (Iron Man) escapes from captivity with his home…
rallain | December 30, 2008Just to be clear, Newton probably didn't have a portable video camera. I do. I have one of these Flip Mino pocket cameras. Very nice. You can put it in your pocket. However, there is a problem with cameras like these (think of video from camera phones). The problem is the mass, it is too small.
Video from a camera phone or small portable camera looks too jerky (unless you are careful). Sometimes it is jerky to the point that it makes me feel barfy. The reason this happens is that with a small mass, a force can cause a significant acceleration. Let me draw a picture (you know I like…
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…
rallain | December 19, 2008I have been searching for where I found this link, if it was your blog please forgive me for not linking. Here is a link to Common misconceptions in science from wikipedia. Looks fun. Really, I am just posting this so I won't forget to come back to it sometime.
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 14, 2008I saw this over at ScienceGeekGirl which links to a video from two high school chemistry teachers in Colorado. The two teachers describe how they modified their chemistry courses. ScienceGeekGirl gives an excellent summary of their changes and motivations, so here is the short and dirty version:
They realized that their traditional lecture based course was not very effective.
They made video podcasts of their lectures and used class time for the students to work on problems and do demos and stuff.
Really, that is it. It seems so simple, but it is very interesting. The part I find…
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…
rallain | December 11, 2008I was going to go to school and give a final. I guess that is not going to happen now. My daughter measured 7 inches of snow - in Hammond, Louisiana (50 miles from New Orleans). Here are some pictures - more to come (plus video).
From Winter Storm 2008
From Winter Storm 2008
From Winter Storm 2008
rallain | December 10, 2008There is something that has been bothering me about students learning in college. The question is, how much do I treat students like adults and how much do I treat them like children? I have been leaning towards treating them like adults. For example: do I require them to come to class? Right now, no. I think they are adults and should choose whether they come to class or not. Do I require them to do homework? No. Again, I recommend homework (and I actually let them count it for part of their grade if they so choose). So, I give students the ability to choose what to do.
In…
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…