rallain | September 6, 2008So, I am still in Alabama because of lack of electricity in Louisiana (although we got power back last night - YAY!). My wife convinced me to go out and hear this band since we are staying at my parents and they said they would watch the kids. In general, I am way too old and crotchety to go out - but it appears I had no choice. Overall, it was not too bad except for staying out too late. (the band was actually pretty good - I think they were called [Fly By Radio](http://www.fly-byradio.com/) and they played 80s musics) The one thing I thought about while in the bar was the long line of…
rallain | September 5, 2008**pre-reqs:** [kinematics](http://scienceblogs.com/dotphysics/2008/09/basics-kinematics.php)
My previous "basics" post was on kinematics (in one dimension). But what about two dimensions? In particular, what about projectile motion. My motivation here is that I was about to talk about analysis of a video that involved projectile motion and I don't want to go over all the stuff again and again.
Let me start with a generic, one-dimensional kinematic equation:
This relates the position (s), the velocity…
rallain | September 4, 2008One of my daughters was just reading Chicken Little to me. I don't know if you are familiar with Chicken Little, but she is a chicken that runs around telling people "The sky is falling". In my normal fashion, I started thinking about the plausibility of this. What would fall? What would you look for? Then I figured it out. The sky IS falling. It is ALWAYS falling and it has always been falling.
What is the sky? I am assuming the sky is the air. I will treat the air as a gas of single particles (which it isn't, but that's ok). So, why does this sky (air) do what it does? If you…
rallain | September 3, 2008**pre reqs:** *none*
Often I will do some type of analysis that I think is quite cool. But there is a problem. I keep having to make a choice. Either go into all the little details, or skip over them. My goal for this blog is to make each post such that someone could learn some physics, but I also don't want it to go too long. So, instead of continually describing different aspects of basic physics - I will just do it once. Then, when there is a future post using those ideas, I can just refer to this post. Get it?
Fine. On with the first idea - kinematics. Kinematics typically means…
rallain | September 2, 2008Here I am, at my parents house. There is no power at my house and Louisiana in September with no power is really a whole bunch of no-fun. But maybe I can use this time to talk about science.
**The Nature of Science**
Here is a review. What is science all about? (I am pretty sure I talked about this before) Science is about making observations and from those observations creating models. If the model predicts other things that are confirmed, then that is good. If not, the model must be changed. Really, it's that simple.
**Hurricane Models**
It is somewhat interesting that forecasting…
rallain | August 29, 2008I teach classes. I ask questions in class. I wait for answers. All faculty do this, so who cares. If you are in a class or teaching a class, how long do you wait for someone to answer your question? Well, I asked two questions of my class this week.
1. Estimate how long I wait when I ask you questions.
2. How long should you (ideally) wait in a class for someone to answer?
Here is the data I gathered: (and I will tell you how long I actually wait)
This is a class of about 30 students. Below is a histogram of how long they estimate I wait for an answer. To make things work out, I…
rallain | August 28, 2008I recently saw a comment on a blog somewhere about putting satellites into space (I think it was from a post about a rocket that blew up). The poster suggested using a giant catapult to put things in space instead of rockets. Maybe he or she was kidding, or maybe not. But I have heard this idea before. Would it work?
First, how do things get in orbit? Orbit is a motion in which the gravitational force on an object makes it move in a circle around another object. In order to be in a circular orbit, it takes a certain amount of energy.
Let me just start with some calculations. How fast…
rallain | August 27, 2008Maybe you can tell I am watching the MythBuster's Moon Special. In the show, the MythBusters go in a plane to reproduce the gravitational forces on the moon. I previously went over this, so here is the link:
[Tutorial on how gravity and weightlessness (zero-g) work](http://scienceblogs.com/dotphysics/2008/09/gravity-weightlessness-and-a…)
rallain | August 27, 2008Clearly the MythBusters did this before I did (it's just airing tonight though). I just wanted to say that I posted some videos of the Apollo "jump salute" video analysis and also sped it up to "Earth-like" accelerations. I then made a video of my daughter doing the same thing on Earth and slowed it down. Yes, the MythBusters did it better, but I just wanted to say "me too". My analysis is here:
[Undoing Fake Moon Landing Videos](http://www.dotphys.net/files/moon-time.html)
P.S. I also slowed down a video of Kobe Bryant Jumping so he has an acceleration of that on the moon.
rallain | August 26, 2008Heat. You have heard it before. You have used it. I have even used it. Do we need this word? No. Is this a useful word? No.
Let me start with the definition as usually stated in a physics type text: (this is from [dictionary.com](http://dictionary.reference.com/browse/heat))
*heat:* a nonmechanical energy transfer with reference to a temperature difference between a system and its surroundings or between two parts of the same system.
This definition is fine. It is not wrong, but is it needed? Not really. Couldn't we just say energy transfer? Actually, I like to use this in the…
rallain | August 26, 2008I know the olympics are basically over. Really, I should have posted this earlier. Anyway, the gymnastics feat that always impresses me is the Iron Cross (I think that is what it is called). I know you have seen this, but here is a picture from wikipedia:
(http://en.wikipedia.org/wiki/Rings_(gymnastics))
Why is this so impressive? Why is this so difficult? Let me start with something completely different that is exactly the same (in some ways).
Here is a heavy box hung from a rope that has…
rallain | August 25, 2008Dear RapidWeaver,
What did I do to you? I like you, I really do - but this is why we broke up. It's not you, it's me. No wait, it's you. I am looking back through my old dotphys posts and most of my introductions are GONE. I was starting to think I was crazy when I wrote these. Take for instance [My analysis of Kobe Bryant's Jump](http://dotphys.net/files/kobe.html). Isn't it odd how this starts? That is because it is MISSING the first paragraph. The only reason I know I am not insane is because of Apple's Time Machine. I went back and looked and the older file has an intro.…
rallain | August 24, 2008I can't believe there is still all this talk about what to call Pluto. Can't we just move on? In an effort to help, I have summoned the Zombie Feynman to get his words on the subject. This is what he said:
"We (my father and I) used to go up to the Catskill Mountains for vacations. In New York, you go the Catskill Mountains for vacations. The poor husbands had to go to work during the week, but they would come rushing out for weekends and stay with their families. On the weekends, my father would take me for walks at night. He often took me for walks, and we learned all about the sky, and…
rallain | August 23, 2008As you may or may not have noticed, I have been using RapidWeaver for my blogging posts. (if you don't know what that is, it doesn't matter) Anyway, I think my stuff was getting a little too big for that software. It was a great place to start, but it is time to move to something else (WordPress). My plan is to keep http://www.dotphys.net as it is so that if you linked to something there, it will still be linked. Also, I will use dotphys.net to post longer tutorial style things. I will likely move some of my favorite posts over to this, but that will take some time (but it will give me…