How much lift does a 12in Helium Balloon give?

Question

I need to weight down a group of three 12in Helium Balloons.

Each Balloon contains 100 litre of helium, and weighs around 12 grams.

What is the minimum mass I can use as a weight for them?

Answer 1

http://answers.yahoo.com/question/index;...

similar question

Answer 2

It's difficult to be precise because of variation due to pressure, temperature and so on, but if you want a rough idea:

A balloon with a volume of 100 litres will displace 100 litres of air.  100 litres of dry air weighs about 127 grams, so by Archimedes's principle this will be the upthrust on the balloon.

From this you must deduct the weight of the helium, and the weight of the fabric of the balloon.

100 litres of helium at standard pressure and temperature weighs about 17.8 grams.  You say your balloon weighs 12 grams

The net upthrust on one balloon will therefore be about

127 - 17.8 -12 = 97.2 grams

Your three balloons will therefore (almost) lift about

3 * 97.2 = 291.6 grams (about 10.29 ounces))