# Denisity of air

1. Feb 22, 2009

### nour naser

i want to know about the denisity of air and how does it exchange .... to use it in equation ....and the denisity of helium .... and how much do we need helium ( i mean volume ) to elevate 1 kg weight ... thank u sooo much

2. Feb 22, 2009

### HallsofIvy

Last edited by a moderator: Apr 24, 2017
3. Feb 22, 2009

### pallidin

I think the OP might be asking:
How much helium within a balloon is required to lift a payload of 1 kg.

The following is from: http://www.howstuffworks.com/question185.htm

If you have read the article How Helium Balloons Work, then you know that helium has a lifting force of 1 gram per liter. So if you have a balloon that contains 5 liters of helium, the balloon can lift 5 grams.

A normal balloon at an amusement park might be 30 centimeters (about 1 foot) in diameter. To determine how many liters of helium a sphere can hold, the equation is 4/3 x pi x r x r x r. The radius of a 30-centimeter-diameter balloon is 15 centimeters, so:

4/3 x pi x 15 x 15 x 15 = 14,137 cubic centimeters = 14 liters

So a normal amusement park balloon can lift about 14 grams, assuming that the weight of the balloon itself and the string is negligible.

If you weigh 50 kilograms (about 110 pounds), then you weigh 50,000 grams. Divide your 50,000 grams by the 14 grams per balloon and you find that you need 3,571.42 balloons to lift your weight. You might want to add 500 more if you actually would like to rise at a reasonable rate. So you need roughly 4,000 balloons to lift yourself if you weigh 50 kilograms, and you can adjust that number according to your weight.

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That should give you enough info...