Physics
rallain | September 13, 2008There is no air resistance in line rider. Sorry to spoil the suspense.
To test for the presence of an air resistance force, a track was created that let the rider fall.
(note the markers on the side. These are used to keep track of how the origin is moving).
Below is the y position of the rider as a function of time:
In this situation, the rider falls about 100 meters. A quadratic line is fit to the data…
rallain | September 13, 2008Scale of the Line Rider
First, we assume that the line rider is on Earth and for low speeds will have a free-falling acceleration of 9.8 m/s2. Next, an arbitrary distance is selected. In this case the length of the sled is chosen to be 1 LU (Linerider Unit).
The goal will be to put the linerider in a free fall (where air resistance should be able to be ignored) and determine his (it could be a she, it is difficult to tell) acceleration in LU/s2. Then we can determine the conversion factor from LU/s2 to…
rallain | September 13, 2008Part I: Introduction
http://linerider.com is a flash "game" in which the user can create tracks. A rider is then allowed to slide down these tracks. If you have not played this, I recommend you DON'T play it. It is very addicting and can consume many hours of your time (hours you would otherwise spend on Digg or surfing needlessly).
In this short report, I will analyze the physics involved in line rider. An obvious question is "why not just ask the line rider programmer?". Well, that would not be too much fun. Would it? So, there is the first reason - its fun. The second reason is to give an…
rallain | September 12, 2008Suppose I am working on a problem and I wish to calculate the density of something. I measure the mass to be *m* = 24.5 grams and the volume is *V* = 10 cm3. In this case the density would be:
ALERT! ALERT! ALERT! This is not a test!!!! Something is drastically wrong! Clearly I messed up. How can I have the mass measured to **3** significant figures, the volume measured to **1** significant figure, but the density calculated to **3** significant figures? Isn't this a violation of some fundamental…
pontiff | September 11, 2008You may have noticed an ad running on scienceblogs which says "Has the LHC destoyed the Earth?" If you click on it you find a webpage that says in big letters simply "NO". What's up with that? Check out the webpage source for the page (http://www.hasthelhcdestroyedtheearth.com/).
Update 9/12/08: Check out the comments for more fun and also read the cat projectile analyzers take on how you can click to save the world.
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Has the Large Hadron Collider destroyed the earth yet?
NO
href="http://www.seedmagazine.com/news/…
rallain | September 11, 2008The MythBusters aren't really doing it wrong, but they give me a chance to talk about some physics. In the latest show, they tested the myth that two phone books with their pages alternating were indestructible. To test this, they put the two phone books together and then pulled them apart in a sort of tug of war. Here is a diagram:
Looks great, what is wrong with this? The problem is that by pulling this way, the MythBusters produces 320 pounds of force on the book - but they could have done twice that. This…
pontiff | September 11, 2008The physics blogosphere is abuzz about the start up of the large hadron collider. There is a hole in Texas which is very jealous. And of course, everyone is happy that the Earth was not destroyed or a bubble universe wasn't created.
But if I remember my science fiction correctly, I don't believe that one can conclude from our continued existence that the LHC isn't making black holes. Indeed if the plot is followed, which is the prophecy equivalent of the derivation being sound, then we will discover that the LHC has produced a trillion mini black holes at the center of the Earth. And of…
drorzel | September 10, 2008We're out for a walk, when the dog spots a squirrel up ahead and takes off in pursuit. The squirrel flees into a yard and dodges around a small ornamental maple. Emmy doesn't alter her course in the slightest, and just before she slams into the tree, I pull her up short.
"What'd you do that for?" she asks, indignantly.
"What do you mean? You were about to run into a tree, and I stopped you."
"No I wasn't." She looks off after the squirrel, now safely up a bigger tree on the other side of the yard. "Because of quantum."
We start walking again. "OK, you're going to have to explain that," I say…
terrasig | September 10, 2008Despite having to employ biophysical methods in my day job, I must admit my woeful understanding of physics as a discipline. I wasn't like my high school grease monkey friends using torque wrenches on their cars with Springsteenonian dedication and my lowest grade in undergrad came in physics. For that reason, I rarely have the opportunity to link to fellow ScienceBlogger, Chad Orzel of Uncertain Principles. Prof Orzel was one of the earliest science bloggers, coming online in June, 2002.
Chad posted about being on the programme of a meeting in Waterloo, Ontario, entitled, "Science in the…
drorzel | September 8, 2008I gave my talk this morning at the Science in the 21st Century conference. Video will eventually be available at the Perimeter Institute Recorded Seminar Archive site, but if you'd like to get a sense of the talk, a few people were live-blogging it in the FriendFeed room for the meeting. You get a pretty accurate impression of the talk from the comments there.
I think it went well. People laughed in the right places, and there was some really good discussion in the question period. I look forward to seeing what it looks like on video. They have a really nice AV set-up here, with two cameras…
rallain | September 6, 2008Here is the video in question:
Looks too incredible to be real for me. That is when I start to question things. Is this fake or not? To answer this, I took a clip that showed a person launching a grocery item over the isle. This was a good shot to look at because it was *mostly* perpendicular to the camera view. I then used [Tracker video analysis (free) tool](http://www.cabrillo.edu/~dbrown/tracker/) to get x-y-time data for the flying projectile grocery. The scale was difficult, so I just guessed that the guy on the left was 5 foot 10 inches. Here is the vertical position data for…
jstemwedel | September 5, 2008In a comment on another post, Blatnoi asks for my take on a recent news item in Nature:
An Italian-led research group's closely held data have been outed by paparazzi physicists, who photographed conference slides and then used the data in their own publications.
For weeks, the physics community has been buzzing with the latest results on 'dark matter' from a European satellite mission known as PAMELA (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics). Team members have talked about their latest results at several recent conferences ... but beyond a quick flash of a…
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…
purepedantry | September 2, 2008In honor of the opening of the Large Hadron Collider at CERN, Michigan State University graduate student Kate McAlpine has an LHC rap on YouTube. The best part: the science is dead on.
Hat-tip: NPR
drorzel | September 2, 2008This was the last of the experiments that I did for my thesis (it's not the last xenon paper I'm an author on, but the work for that one was done while I was writing up), so my memories of it are bound up with the thesis-writing process.
My favorite story about this stuff was when I gave a talk about this work at NIST-- I don't recall if it was before or after my defense-- and somebody asked the obvious question about how the quantum statistical rules are enforced. That is, how is it that you never get two identical fermions colliding in an s-wave state? Since an s-wave collision is just a…
pontiff | September 1, 2008David Wineland, laser cooling god and ion trap quantum computer builder extraordinaire, has been awarded the National Medal of Science. Much awesomeness.
Also winning the medal this year is a name familiar to computer scientists and engineers worldwide, or simply who have spent time at USC: Andrew Viterbi, inventor of the Viterbi algorithm and cofounder of Qualcom, among other notable achievements.
drorzel | August 30, 2008Over at Built om Facts, Matt is working toward a Tope Ten list of physicists. He says the top three are obvious, but he's soliciting nominations for the rest.
Back in the early days of this blog, I ran a poll for the greatest experiment in physics, and there are worse places to start. Newton and Galileo are two of the obvious three (Einstein is the third), and I think Rutherford and Faraday absolutely belong on the list (Faraday gets bonus points for his interest in outreach to a wide audience). If you want to keep astronomy in with physics, Hubble belongs as well.
Broadening things to…
drorzel | August 29, 2008As anybody who has studied Quantum Optics knows, correlation functions play a very large role in our understanding of the behavior of light. Roughly speaking, the correlation function tells you how likely you are to detect a second photon some short time after detecting one photon from some source. This shows up in the famous Hanbury Brown and Twiss experiment, and definitive proof of the existence of photons was provided in 1977 when Kimble, Dagenais and Mandel demonstrated photon anti-bunching, where the correlation function goes to zero for short times.
Correlation functions are a powerful…