Physics
esiegel | August 6, 2009Every once in awhile, a question makes it to my inbox that's too good to ignore.
A friend and I were joking about being "older than dirt" and he asked a question I thought you might enjoy: "Hey, ask Ethan how old dirt is and how it got here."
You did the smart thing by coming to me, because the alternative is to ask yahoo. (Shudder!) Well, right away, we've got an upper limit, because the entire Solar System is only about 4.5 billion years old. So, there's no way that this:
is any older than this:
Now, you can definitely go looking for the oldest rocks on Earth, and if you look very hard,…
rallain | August 6, 2009Thanks to Nick for showing me this video (Check out his blog - Fine Structure):
See more funny videos and TBT Videos at Today's Big Thing.
Wow. That was my first reaction. My second reaction was: no way. Is this real life? I just don't know. How hard would it be to find out exactly where to place that pool and where did they get the water from? Obviously, this one requires some analysis. First, on the VAS for this video: 4/8. Not too good. Oh here are the questions I would like to answer:
What is the guy's acceleration after he leaves the ramp?
What was his initial velocity…
pontiff | August 5, 2009Booz Allen Hamilton is looking for a science and technology consultant in quantum information sciences. Help be a part of quantum revolution! Description and contact info below the fold.
Key Role/Position Description:
Serve as a strategic consultant to government science and technology clients. Contribute to advancing the state-of the-art in the quantum sciences by combining strategic planning and technical analysis. Assist clients in researching and formulating ideas for new research programs. Provide expertise in assessing research proposals for technical merit and proposal objectives.…
rallain | August 5, 2009I keep saying the same stuff over and over when it comes to analyzing videos. I can't immediately find a post that lists what makes a video acceptable for analysis, so I will just reproduce on here. I will give 1 point for each of the following that the video has:
Stationary camera and background
Camera does not zoom
Motion perpendicular to the camera
You can see the object in every frame (nothing obscuring the motion)
Interesting physics content
Downloadable (some videos I can't "get off the web")
No repeating frames
Not badly interlaced (or would that be deinterlaced - I get confused)…
rallain | August 5, 2009Parkour: the act of running and jumping like a crazy superhero. I can't do any of it. But I can analyze it. So, let me start with the wall-flip (or any kind of move that involves walking on vertical walls). This looks like a good example (there are a bajillion on youtube).
Pretty cool, huh? How do you run up a wall? Well, it has to do with friction. Remember, this is a fairly useful model for the magnitude of the frictional force on an object:
Where N is the force the surface exerts on the object (the normal force) and ?s is the coefficient of static friction. Note that this less…
rallain | August 4, 2009Check this out (saw it on the interwebs):
It's this video inside a bus of a girl hitting the roof. My first thought was: well, she just jumped. But something was odd. She was in the air too long. Well, of course this calls for a video analysis (using Tracker Video Analysis). Actually, it is a good candidate for analysis. Primarily because the motion happens right next to the back of the bus and the bus can be considered the reference frame. The only problem is the scale. I totally guessed that the back window was 3 feet, but not sure this even matters. Here is the motion of the girl…
esiegel | August 3, 2009At the end of last week, I wrote a post explaining how the Universe is so big (93 billion light years across) when it's only 13.7 billion years old. The key visualization is to think of space as being the surface of an expanding balloon, while all the things in the Universe (stars, galaxies, etc.) are like ants on that surface.
Now, I explained to you that two ants will appear to move apart from one another due to the expansion of the Universe, even though neither ant is moving relative to the surface of the balloon. If I use light to measure whether this other ant is moving away from me, I…
rallain | August 3, 2009Every introductory astronomy text and most intro physics texts talk about tides. The usual explanation is something along the lines of:
The moon exerts a gravitational force on the Earth and all the stuff on the Earth.
This force decreases with distance (1/r2).
Thus the moon pulls greater on one side of the Earth than the other
This doesn't matter except for oceans which can move.
BOOM. Two tides a day due to a bulge on the side close to the moon and the opposite side.
Oh, the Earth is slowing down.
Really, that is what almost all intro texts say. Go check for yourselves.
Yes, the tides…
drorzel | August 3, 2009Last weekend, I was talking with Ethan Zuckerman at a party, and we talked a little bit about the TED conferences and similar things. A few days later, there was an editorial in Nature suggesting that scientists could learn a lot from TED:
[P]erhaps the most critical key to success is the style of the talks. And here, those scientists wishing to inspire public audiences could take a few tips from the speakers in Oxford who addressed themes as various as biomimicry (Janine Benyus), the neuroscience of other people's rational and moral judgements (Rebecca Saxe) and supermassive black holes (…
esiegel | July 31, 2009I get a certain question every so often, and it's one of the most difficult questions any cosmologist faces. Today, I try to tackle it. It goes something like this:
If the Universe is 13.7 billion years old, and nothing can go faster than the speed of light, how is it that we see things that are 46.5 billion light years away?
First off -- and I want to clarify this -- everything in this question is legit.
1.) The Universe is 13.7 billion years old. There are small errors there -- no one would be surprised if it was 13.5 billion or 14.0 billion years old -- but it's definitely not 12 billion…
drorzel | July 31, 2009Yesterday's historical physics poll was about precision measurements. Who were those people, and why are they worth knowing about?
As usual, we'll do these in reverse order of popularity...
First up is Ole Rømer, a Danish astronomer who is no stranger to this blog, having been profiled as part of the Top Eleven series back in the early days of ScienceBlogs. Rømer's big accomplishment was the first really good measurement of the speed of light, which he did by timing the eclipses of Jupiter's moon Io. These are seen to occur slightly sooner when Earth and Jupiter are on the same side of the…
drorzel | July 31, 2009I had a bit of a discussion via Twitter with Eric Weinstein yesterday, starting with his statement:
Ed Witten has no Nobel Prize. Now tell me again how this era's physics just feels different because we are too close to it.
Basically, he appears to feel that Witten is sufficiently smart that he ought to have a Nobel. My feeling is that if you look at the list of Nobel laureates in physics, you won't find any theorists who won before their theory had experimental confirmation. It's not an official rule, but it seems to be well established practice.
My attempt at an analogy was the late John…
rallain | July 30, 2009The fall semester is coming up soon. Some students will be taking physics in college. So, here are some pre-class tips - mainly aimed at college students taking algebra-based physics.
Are you afraid?
If you are reading this, maybe you found it because you were looking for stuff on physics. Maybe you are a little scared. You have heard physics is a tough course. Well, that is only kind of true. First, the fear thing. Use it to your advantage. Let fear be a motivator to help you keep up with the class. I think that is the biggest mistake students make. They think of intro physics as…
drorzel | July 30, 2009Keeping up the string of poll questions about less-well-known physicists (started here), here's a list of physicists who are known for having made very precise measurements of physical quanitites. Which of them is the best?
Which of these physicists who made precision measurements is the best?(poll)
(Note: I have deliberately limited this to physicists who are no longer alive, which is why some recent names are missing.)
drorzel | July 30, 2009Yesterday, I posted a silly poll about optical physicists. Who are those people, and why should you care about them?
In inverse order of popularity:
Bringing up the rear in this race is John William Strutt, who, even more than Lord Kelvin in the thermodynamics poll, is hurt by the fact that people know him by his title, Lord Rayleigh. His notable achievements in optics include a formalization of the resolution limits for optical devices, and the phenomenon known as "Rayleigh Scattering," which is the short answer to the question "Why is the sky blue?" (The long answer requires a whole book.)…
rallain | July 29, 2009I am not a programmer. Just to be clear. I use python to get things done, but I am sure it could be done in more efficient ways. Anyway, I sure you know how much I like vpython - especially for teaching physics. However, sometimes I use it for blogging stuff also. The problem is that vpython doesn't make pretty graphs. Oh, they are quick and simple - but sometimes you want pretty also. Well, what if you just don't use vpython? Of course then I could use some other plotting package like pylab (which actually uses something else like matplotlib or something - I get confused). Or, I…
rallain | July 29, 2009You have no idea how long I have been sitting on this one. I made some videos like a billion years ago, and still no post. Why? Oh well, here it is.
I like video analysis of motion. I like looking at stuff on youtube or other video sites. But sometimes, you need to make the video yourself. What should you use? My personal favorite is a Flip Mino HD. It is small and quick. Are there other options? Sure. In this post, I will do the video analysis with the following cameras:
Flip Mino HD
A Canon PowerShot A470
Panasonic DMC-FZ18
Canon HV10 HD miniDV camcorder (you know, the kind that…
drorzel | July 29, 2009In the same basic vein as yesterday's post about thermodynamics, the following poll contains a list of physicists who are not household names, but who made significant contributions to the science of optics. Which of them is the best?
Which of these physicists from the field of optics was the best?(polls)
drorzel | July 29, 2009The Corporate Masters have launched a "featured blogger" program, asking individual ScienceBloggers to comment on news articles from the main site, and publishing the responses with the magazine piece. I just did one on new quantum experiments, which was posted today.
The news article is Supersizing Quantum Behavior by Veronique Greenwood. My piece is Reconciling an Ordinary World, which starts out:
One of the most vexing things about studying quantum mechanics is how maddeningly classical the world is. Quantum physics features all sorts of marvelous things--particles behaving like waves,…
drorzel | July 29, 2009So, yesterday featured a silly poll about underappreciated old-timey physicists. Who are these people, and why should you know about them?
Taking them in reverse order of the voting:
Rudolf Clausius is the originator of the infamous Second Law of Thermodynamics, which states that the entropy of any closed system will tend to increase. He was one of the most important figures in terms of systematizing the study of thermodynamics, pulling a lot of other people's work together, and showing how it all fit.
James Joule was a brewer as well as a physicist, making him a really good guy to know. He's…