# I am lightest on the ground but I am heaviest in the air

I am lightest on the ground but I am heaviest in the air. What am I?

I'm going to say

Fog

Lightest on the ground

Cloud floating on the ground

Heaviest in the air

Cloud sinking to the ground

It could be a

Hot air balloon

It's lightest on the ground because

the air outside the balloon is heavier than inside. This is due to the higher temperature inside the balloon, thus lower pressure than outside the balloon.

It's heaviest in the air because

the atmospheric pressure is lower higher up (i.e. the air is lighter), making the balloon relatively heavier.

Otherwise it would just go up up up.

My guess is

CO2

Lightest on the ground

Lots of CO2 is trapped in our soil through various means. It is among the lightest compounds found in soil.

Heaviest in the air:

CO2 is the heaviest compound (that I know of) in the Earth's atmosphere. I believe Argon is the second heaviest, with an atomic weight of 18, but I could be mistaken.

Could it be

Gravity

Reasoning:

The perception of gravity on the ground is not really thought of, however when one jumps, for example, the perceived pull of gravity is far heavier.

• I'd argue against that by nature of the fact that gravity actually (in terms of physics) becomes weaker the further you move away from the ground (assuming that the ground is the source of that gravity) – NegativeFriction Jan 13 '20 at 16:06
• Definitely true, however, I am pointing out the perception of it. – ProNoob Jan 14 '20 at 8:41

Is it

A meteor?

Reasoning

Meteors are heaviest in the air, but lightest when they hit the ground (as a meteorite) because of the matter lost as its outer layers disintegrate into the atmosphere.

You are air, because it is on the ground and in the air, if you were anything else than air (heavier or lighter), the two statement wouldn't be true at the same time, because either air would be lighter on the ground, or air would be heavier in the air.