estimation
rallain | August 23, 2009I saw this video on digg or reddit. I can't remember which.
I was in awe. Then I started thinking. I wonder how fast that water was moving up right after the explosion. Too bad the video doesn't have a scale. Well, it kind of does - there is that ship. I am terrible at ship identification though. Maybe I can use my favorite scaling trick - assume the stuff is on the surface of the Earth. This means that free falling objects would have an acceleration of -9.8 m/s2. Let me try this on the water as it falls. Oh, trust me. I know it is not really free falling, but it is in this big…
rallain | June 23, 2009This was on my 'to do' list, but Tom at Swans on Tea beat me to it. Basically, this grocery store has these plates that when depressed produce electrical energy. Tom does a good job pointing out that this is not free energy (the original article says this also). Clearly, the energy comes from the cars. How much would this cost the cars?
As always, let me start with some assumptions.
The original article says that the bumps will generate 30 kW of energy every hour. That is an odd thing to say. I am going to interpret that as 30 kW of power for all hours (every hour). They couldn't have…
rallain | June 9, 2009So, analysis of the movie Up is pretty popular in the blogosphere. Figure I might as well surf the popularity wave. So, I have a couple more questions.
The most important thing to estimate is the mass of the house. I am going to completely ignore the buoyancy of the house. I figure this will be insignificant next to the buoyancy needed. Anyway, let me go ahead and recap what has already been done on this in the blogosphere.
Wired Science - How Pixar's Up House Could Really Fly - from that post:
First, they calculated (seemingly correct) that the buoyancy of helium is 0.067 pounds per…
rallain | June 3, 2009I haven't seen the Pixar Movie "Up" yet, so don't spoil it for me. I have, however, seen the trailer. In my usual fashion, I have to find something to complain about. There is this scene where the old man releases balloons out of the house.
What is wrong with this scene? Also, would that be enough balloons to make the house float? Here is a shot of the balloons coming out of the house.
Ok, I was already wrong. The first time I saw this trailer I thought the balloons were stored in his house. After re-watching in slow motion, it seems the balloons were maybe in the back yard held down…
rallain | April 28, 2009In the second Cat in the Hat book (I think it is the second one), the Cat reveals that he has more smaller cats under his hat. They are labeled A - Z with Z being so small you can't even see. Question: What is the sequence of sizes for successive cats? How big would Cat Z be?
Here is the first picture that Cat reveals Cat A. It is not trivial to measure their relative sizes because they are in different positions. I drew two circles, one around each head and looked at the circle sizes.
So, Cat has a head that is 165 px tall and Cat A has a head 61 px tall. Let me call the total length…
rallain | March 4, 2009Some time ago, I wrote about the awesome things the Greeks did in astronomy. Basically they calculated the size of the Earth, distance and size of the moon and distance and size of the sun. The value obtained for the distance to the sun was a bit off, but still a bang up job if you ask me. (where bang-up is meant as a good thing) If the greeks were in my introductory physics lab, they would need to include uncertainties with their measurements. What would the uncertainty in the final value look like?
In my introductory physics lab course, I have students measure things and estimate the…
rallain | February 12, 2009Since this could be current events, I am reposting my analysis of space debris in the movie Wall-E.
Here is a shot from the scene where the space craft is leaving Earth:
In this scene, the spacecraft has to break through all the Earth-based space debris. The first problem is that the unused satellites are just sitting there. If they were to stay in orbit, they must move. Maybe the WALL-E creators are sticking with the no air means no gravity idea. At least they are consistent.
The other problem with that scene is the sheer amount of junk in orbit. Suppose that was 300 km above the surface of…
rallain | December 6, 2008This comes from Buzz Out Loud Episode 865 which got the story from Slashdot regarding a possible new technology that would use piezoelectric devices to charge cell phones while you talk. The original article the slashdot story pointed to talked mostly about the advances in piezoelectric devices, but I want to look at the possibility that sound could charge a phone.
First for the basic physics. How do you make sound and what is it? Sound is a compression wave in the air. To make a sound you need something to push the air (yes, I simplified this quite a bit). When that something pushes the…
rallain | October 2, 2008Gas prices may be trending down, but they are still quite high. How can we save gas? One of my colleagues suggested we can save gas by getting rid of all drive throughs. This means it is my job to estimate how much could be saved.
**Starting Assumptions (estimations)**
How many drive-throughs are there in the U.S.A.? When I think of drive-throughs, I think of McDonalds. [Wikipedia](http://en.wikipedia.org/wiki/Mcdonalds) says there are 31,000 restaurants world wide. I am going to say there are around 20,000 in the U.S. that have drive-throughs. So then, how many total drive-throughs?…
rallain | September 30, 2008Which wastes more fuel? (and thus produces more carbon dioxide). This is a difficult to question to answer for a variety of reasons. The main reason is that a speed change from 71 mph to 70 mph is different than a reduction from 56 to 55 mph.
First, let me be clear that the question of how much fuel is wasted using daytime running lights (or DRL as they are called) has already been addressed. The first source I found was howstuffworks.com
**Assumptions**
The daytime running lights on a car run at about 100 watts (for the pair)
The energy density of gasoline is 1.21 x 108 Joules/gallon.
A car…
rallain | September 28, 2008When mowing the lawn, I like to listen to podcasts. One of my favorites is [Buzz Out Loud](http://bol.cnet.com). This weekend, I was listening to episode 817 and one of the topics of discussion was MySpace and their DRM free music stuff. [Wired](http://blog.wired.com/music/2008/09/myspace-launche.html) had a description of what they were going to do. That is not my point. The point is the claim that you could make an infinite number of playlists. How about I calculate (or estimate) the number of different playlists one could make.
First, the idea behind the idea. Calculating the number…