velocity
rallain | December 4, 2008Ok - I like Alabama football (sorry, but it's true). There is a clip on youtube of the end of the Alabama-Auburn game where the fans sing the traditional "Rammer Jammer". If you don't know what that is, don't worry. I am not sure I completely approve of the cheer, but it is a tradition. If you are curious, here it is:
So, what is cool about this? Notice that the entire crowd is yelling the same thing, but they are out of sync. Can this be used to estimate the size of the stadium?
I made an audio file from that youtube clip and looked at it with Audacity. Although I am completely…
rallain | September 24, 2008**pre reqs:** [Vectors and Vector Addition](http://scienceblogs.com/dotphysics/2008/09/basics-vectors-and-vector-ad…)
This was sent in as a request. I try to please, so here it is. The topic is something that comes up in introductory physics - although I am not sure why. There are many more important things to worry about. Let me start with an example. Suppose you are on a train that is moving 10 m/s to the right and you throw a ball at 5 m/s to the right. How fast would someone on the ground see this ball? You can likely come up with an answer of 15 m/s - that wasn't so hard right?…
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…
esiegel | May 8, 2008Let's say we're having a nice day here on Earth; the Sun is shining, the clouds are sparse, and everything is just looking like a peach:
And then Lucas goes and tells me,
Oh my God, Ethan! It's Armageddon! An asteroid is coming straight for us! You've got to stop it!
Really? Me? Well, how would I do it? Let's say we've got some reasonably good asteroid tracking going on, and we've got about 2 months before the asteroid is actually going to hit us. We'd like to do something with the situation on the left, to avoid the situation on the right:
Well, what we really have to do is change the…
esiegel | April 10, 2008In a comment on my last post, What is Dark Energy, Kendall asks the following, which is such a good one I think it deserves its own post:
I thought the expansion was accelerating? Aren’t you saying that it is on its way down to 85% of its current rate? Sounds like expansion is slowing, but still leaves us with an open universe…
People do say the expansion of the Universe is accelerating. But that doesn't mean that the expansion rate is accelerating. It means that if you take a look at any one galaxy that isn't gravitationally bound to us in the Local Group (that is, any big galaxy that isn't…
esiegel | February 27, 2008The Moon goes around the Earth, the Earth goes around the Sun, and the Sun goes around the center of the Milky Way. We know the Moon takes about 4 weeks to make its trip around the Earth, and that causes the Moon phases:
We also know that the Earth takes one year to go around the Sun, and that causes the seasons:
We also know that the Earth has been around for about 4.5 billion years, which means it has gone around the Sun about 4.5 billion times. Well, now I ask the question(s):
How long does it take the Sun to go around the Milky Way? How many times has it done that so far, and how many…