Why do liquid molecules spread?

Header: Water and Air: What Makes the Difference?

Why is water liquid?
The water molecules are built in such a way that they attract each other about ten times more than the gas molecules in the air. A small difference with major consequences: Water therefore condenses into a liquid, while air only begins to become liquid at extremely low temperatures of less than –180 degrees Celsius.

What is harder?
It's hard to believe, but water is actually lighter than air. A single water molecule weighs less than the average air molecule. This is why moist air rises so well and forms clouds at high altitudes. But in its liquid state, water is significantly heavier. The water molecules are packed a thousand times closer together in the liquid - a liter of water therefore weighs almost a thousand times as much as a liter of air.

Where is it warmer?
25 degrees Celsius feels warm as long as you are in the air. Quite different in water: You get cold there quickly. Because water dissipates our body heat from us a hundred times better. The reason here too: the higher particle density. When we are in the water, many molecules lie close to our skin. And they dissipate more body heat than the few molecules that touch us outside in the air.

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Where is the sound faster?
Sound waves propagate through collisions between molecules. And since these are very tightly packed in the water, they quickly pass the sound shocks on to one another. The air molecules are further apart: things are slower there. This means that sound in water is around four times faster than in air.

Next time, ZEIT Wissen and the "Kopfball" reporters will examine a very special difference between the sexes: Who is tickler - women or men?