# fermi

### Size of 91,000 documents

Here is a quick one. One of the big news stories recently was this regarding WikiLeaks and the release of the Afghan War Diary. There could be tons of things to discuss regarding this - but I am not going to do that. The first thing that struck my mind was "over 91,000 documents". That seems like a lot. If each one of these documents were printed on one page, how big would the stack of paper be? I could just estimate this - fermi-problem style. But instead, I thought would use a stack of paper. Here is a pack of 500 sheets of paper. Opening it, I can measure the thickness: How thick…

### An estimation problem for math teachers

You thought I was going to talk about a problem that math teachers could use, didn't you? Well, maybe math teachers can use this. (note: when I say "teachers" I really mean "learning facilitators") It all started when I read this valedictorian speech from Erica Goldson. Here is part of it: "I am now accomplishing that goal. I am graduating. I should look at this as a positive experience, especially being at the top of my class. However, in retrospect, I cannot say that I am any more intelligent than my peers. I can attest that I am only the best at doing what I am told and working the…

### How fast is the Beacon of Gondor?

The Lord of the Rings trilogy came on TV again recently. My wife and I can't help but to watch this even though we have it on DVD. Anyway, I was thinking about the part where Gondor sends a signal to Rohan asking them for military aid. Since this was before the invention of email, they had to do it with a signal fire. Hopefully this clip won't be a spoiler for you, but this is from the movie. Actually, all of the clips available have embedding disabled. So this is just a picture of that clip. If you want to see it, go to the youtube version. One other spoiler: Sauron is really Frodo's…

### Black Dress: chance or conspiracy?

Here is part of a picture some of my friends posted from a recent high school reunion. It may be hard to tell, but this is part of a picture of 7 females all wearing black. I just wanted to show you that they were indeed wearing black without giving away anymore details. If you are one of these people and you want your whole picture included, I will be happy to make that change and include your face. Anyway, my first comment was: "Wow, everyone is wearing black. Was this a planned event or was black part of the dress code?" The response was that it was just pure chance that all the women…

### Oil Spill Estimation

I was going to just leave the oil spill in the gulf topic alone. Not because it isn't important, obviously it is. Rather, I wasn't going to do anything because I didn't really have anything to add to the topic. After a couple of readers requested it, I think I do have something to add. How exactly do you estimate the amount of oil flowing into the gulf? What do I have to start with? A video. Here is a video of the undersea oil leak. Now, I am not the first to estimate the oil flow rate (NPR on Purdue Prof's estimation and here a commenter make a quick calculation). Like I said, I am…

### Ask a Science Blogger: Insect view

ScienceBlogs.com is running "Ask a Science Blogger". The basic idea is that you, the reader, get a chance to ask questions to us, the bloggers. You can either post a comment in the link above or send an email to . I would like to go ahead and answer one of the questions already posted. nemski asks: How big does the world appear to an insect? I like this question because it can be answered at different levels. First, what do you mean by world? If you mean "the Earth", then the answer would be that the Earth essentially appears the same to an insect as it does to us humans (from a size…

### Could cars slow down the Earth?

Time for another Fermi problem. There was a recent story in Science News that talked about the effects of the Chilean quakes on the Earth's rotation. The basic idea is that some ginmourmous amounts of rock moved closer to the Earth's center. Since the angular momentum of the Earth is conserved, the angular rotation rate would increase. The estimated change of the day was by about 1.26 microseconds. Could all the cars in the USA be used to change the rotation of the Earth? Well, I shouldn't have phrased the question that way. Of course 1 car technically is all you need to change the…

### How many people to review youtube videos?

There was a Buzz Out Loud episode in the not-to-distant past where the discussion of youtube came up. I can't remember the exact details, but the main point was that it would be impossible for google (the owners of youtube) to review all of the videos that were submitted. And here is my calculation. How much would it cost google a year to do this? First, I need to pick some variables (and I will first do this symbolically - then you can put in your own values if it makes you happy). Submission Rate (s): This is how many minutes of video are submitted each minute (so the units would be…

### Physics and the movie UP - floating a house

I 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…

### Energy and charging an electric motorcycle

I just realized that something has been bothering me. It is this KillaCycle - the electric zoom-fast motorcycle that I posted about previously. It clearly is super fast. However there are two claims that seem iffy. It can be recharged in 4 minutes. It is recharged by wind power. It may be possible that these individually could be true - but could it be recharged in 4 minutes by the wind? I am not sure. Let me do some estimations to see if this is possible. What am I starting with: From the review on gas2.org, uses cordless drill batteries. Uses 1200 batteries Produces 500 bhp - not…

### Charging a cell phone with sound - possible?

This 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…

### How much gasoline could we save by stopping drive-throughs?

Gas 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?…

### Turn off daytime running lights, or reduce speed? Which saves more?

Which 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…