Everyday Science

Science of the things and phenomena you come across daily and leaves you in wonder...

[+]What is a nautical mile, and how does it differ from a normal mile and a kilometer?

A nautical mile is based on the circumference of the planet Earth. If you were to cut the Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is 1 nautical mile. This unit of measurement is used by all nations for air and sea travel.

A knot is a unit of measure for speed. If you are traveling at a speed of 1 nautical mile per hour, you are said to be traveling at a speed of 1 knot.

A kilometer is also defined using the planet Earth as a standard of distance. If you were to take the Earth and cut it in half along a line passing from the North Pole through Paris, and then measure the distance of the curve running from the North Pole to the equator on that circle, and then divide that distance by 10,000, you would have the traditional unit for the kilometer as defined in 1791 by the French Academy of Sciences.

A nautical mile is 1,852 meters, or 1.852 kilometers. In the English measurement system, a nautical mile is 1.1508 miles, or 6,076 feet. To travel around the Earth at the equator, you would have to travel (360 * 60) 21,600 nautical miles, 24,857 miles or 40,003 kilometers.

(Courtesy howstuffworks)

[+]Could I power my computer or my TV with a bicycle generator?

To answer this question, you need to know two things:

1. How much power does a computer or a TV consume?
2. Can a person generate that much power with a bicycle?

If you have a normal desktop computer and monitor sitting on your desk, then it probably consumes something around 200 watts. With a bigger monitor, it probably pushes toward 250 watts, but 200 is a good average. A large color TV consumes about the same amount of power.

1 horsepower is equal to 746 watts. So a person would have to generate about 0.27 horsepower to power a computer. Assuming that the generator is not 100-percent efficient, this means that a person would have to generate about a third of a horsepower to run a desktop PC.

If you look at the chart on this page, you can see that, unless you are an Olympic athlete, it would be tough for you to generate a third of a horsepower on a bicycle for any substantial length of time. A "normal person" might be able to sustain a third of a horsepower for half an hour before falling off the bike from exhaustion.

The solution to the problem would be to use a laptop computer instead of a desktop PC. Because laptops are designed to run off batteries, they are very efficient. A laptop might consume 15 watts. It would be extremely easy to generate 15 watts (0.02 horsepower) on a bicycle.

How many calories would you burn doing this? To generate 1 watt for an hour, you burn about 0.85 calories. Rounding up, that's about 1 calorie per watt-hour. So you would burn about 15 calories per hour using your bike to power your laptop. At that rate, a single 60-calorie chocolate-chip cookie could power a laptop for four hours!

(Courtesy howstuffworks)