Helium gas cylinders

[RATTER15]

Does a helium cylinder get heavier as it become empty?

[TeeGee]

I would say no. Helium does have a weight, it's just less than air, so when compressed, a cylinder would weigh more when full than when empty.

[ugly_bob]

In fact, the cannister is never empty. It starts out with compresssed helium, and ends up with helium at atmospheric pressure.

So, in effect, it would weigh less when 'empty' (ie no more will come out) than it would if it was full of air at atmospheric pressure.

[RATTER15]

I see what you are saying but a ballon full of air falls to the floor, where as a balloon full of air is lighter and rises skward!

Im confused!!

[kwicky]

A very interesting question. On a similar vein is a balloon filled with air lighter than a balloon not blown up? The answer surprises me.

http://www.cashflo.co.uk/Air.html

[RATTER15]

Sorry, a balloon full of helium floats skywards

[mibn2cweus]

The principle is displacement. For a given volume (in this case that of the tank) the mass of its contents (along with that of the container) determine whether it will float within the mass of an equal volume (the volume of air it displaces).

If total mass per volume is greater than the mass of the volume it displaces it will sink.
If total mass per volume is less than that of the mass of the volume it displaces it will rise.

Helium at a given pressure is lighter (has less mass) than an equal volume of air under the same pressure.

[RATTER15]

mibn, very impressed but what is the answer to the question?

[curlyfilm]

the helium cylinder will always weigh the same, the helium will weigh less as more is dispersed into the atmosphere, it is the lifting effect of the helium on the cylinder that makes it appear lighter

[mibn2cweus]

My apologies; I was commenting on the thread, not the question which appeared to be answered already. However, if you insist:

There are four factors determining the weight of the helium cylinder:

1. The force of gravity where the weighing is taking place
2. The weight of the cylinder itself
3. The weight of the volume of air displaced by the cylinder
4. The weight of the contents of the cylinder (the helium inside)

Releasing or withdrawing helium from the cylinder would not significantly effect 1, 2, or 3 since any helium released into the air would quickly dissipate upwards (helium having greater buoyancy than air).

This leaves us with only the helium inside the cylinder to consider.
The weight of the helium is determined by its mass, this being the weight of a single helium atom times the quantity of helium atoms inside the cylinder. Therefore, as helium leaves the cylinder, the combined weight of the cylinder and its contents diminishes by the amount of helium released, unless . . .

If the helium from the cylinder is released within a confined enclosure of fixed size (such as a larger sealed tank) the helium (along with any air present) would be compressed until the pressure inside and outside the cylinder reached equilibrium. Under these circumstances the cylinder and the helium remaining inside would experience greater buoyancy and consequently an increased reduction in weight for the amount of helium released.

Either way the answer to your question is �No�. In fact, quite the opposite is true. A helium cylinder can only get lighter as it becomes empty.

Simply stated, removing mass (of any kind) from a given volume of space can only reduce the weight of that volume as measured under a specified force of gravity.

[RATTER15]

mibn, thankyou for your time and knowledge, I see what you are saying now, yes it has been answered above, I was just struggling with it a bit.

Many thanks to you all!!!