# Riddle-like logic question?

Question:If helium is lighter than air, is a helium tank heavier BEFORE you fill it or after?

random question, yet ive been pondering this for a while.

Since you asked the question assuming He gas, I will answer as if the tank has He gas.

Helium gas, lighter than air, tends to rise because the force of gravity pulls down the air more than the Helium. When the air comes down, the Helium goes up.

This phenomena is not applicable when the Helium is trapped in a tank. It can not be displaced by the surrounding air. It pressurizes the tank, and its mass contributes to the weight of the tank.

heavier after.......not filled with gas......LIQUID HELIUM...
It would make sense that because helium is lighter it would make the tank lighter. However, it will most likely be the same weight or even heavier.

The molecules of helium probaby do not have enough lift to pick up the tank at all off the scale. If all of the air is vacuumed out, then there will be nothing inside the tank that helium is trying to get higher than.

Second, the tank was probably at equal pressure inside and out with just the air in it. When they put helium in the tank, they pressurize it, putting in more helium than the air that was in there. Therefore you have more dense helium inside the tank and it would be heavier.

My guess is heavier.
It's heavier if it's filled with compressed helium. It's lighter than a tank filled with air (although maybe negligibly so) if the helium is at normal pressure.
the tank itself is the same weight empty or full
I think it would be heavier afterwards
A tank filled with any gas, including helium, is compressed. Thats why you hear it 'hiss' when you open the valve. When a gas is compressed, it is heavier than what it would be in its natural non-compressed state. More pressure in a tank=more compressed helium=heavier weight.
AFTER.
derpity derp derp derp

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