steam

[dixieland]

if boiling water in a pot evaporates in to steam,why does'nt a puddle turn to steam when the sun heats up the ground

[hairygrape]

Because the water does not reach a temperature of 100 degrees C when heated by the sun unlike the water in the pot.

Yes, the water will warm and slowly evaporate but it won't boil.

[ll_billym]

Water does turn to steam. This is why puddles and indeed whole lakes dry up to nothing when the sun is out for long enough without rain.

You don't see it intensely like the steam you see rising from a pot on the stove as the sun is 90 million miles away and the gas flame is directly on the bottom of the pot but it happens.

[waterboatman]

It does turn to steam. You cannot see steam as it is invisible, what you see coming out of the kettle is water vapour, that is steam which is cooling. If you look at the spout of your kettle when it is boiling (depending on the type of kettle, an old fashioned one with a long spout is best for this) you will see a little clear space between the end of the spout and the cloud of water vapour, that is the steam.
i hope that helps.

[Teddio]

Water boils, producing steam, when its vapour pressure equals or exceeds the atmospheric pressure. For water, this temperature is 100 Celsius when the atmospheric pressure is 101kPa. At lower water temperatures, the vapour pressure is much lower than the atmospheric pressure and the water evaporates, producing water vapour.

[chamois]

Hairygrape and Teddio are both correct whilst the other two answers are wrong.

As Teddio says, water boils when its vapour pressure exceeds atmospheric pressure. This is the only time that it boils.

Everything else is just evaporation.Come on, has anyone seen puddles and lakes drying up to nothing and seen steam coming off them same time? Drying up through boiling is not the same as evaporation.

[ChuckFickens]

Boiling a kettle and a puddle evaporating are excatly the same process, water molecules escape into the atmosphere as "steam" it's only the speed of the process that has been altered by differing amounts of heat.... the more heat the faster it happens and at a point it's fast enough to see clearly as a white mist that is incorrectly called steam (that's just steam condensing in the air)

[chamois]

Fascinating. ChuckFickens would you care to give a scientific explanation of precisely what you mean by "process" in scientific terms so that we scientists can correct what we've been taught for years?

Evaporation and boiling are NOT the same thing. The vapour pressure is what makes the difference.

[chamois]

Incidentaklly, here's a scenario for you. If the water in a puddle is at 10 degrees C and the surrounding air is at 20 degrees C due to heating by the sun, would you expect the puddle to emit steam? Would this steam be visible?

[chamois]

Hmm, on looking at your post again, are you claiming that "speed" accounts for the difference between evaporation and boiling?

[wildwood]

The vapour that rises from the puddle water is still cooler than the surrounding air so it stays invisible - it doesn't turn back into water droplets until it hits the higher colder air and eventually falls back down as rain.
In order for a puddle to show visual evaporation the vapour needs to be so hot that it supersaturated the air such as what would happen if you were to put a pot of warm water outside on a crisp morning.

[heathfield]

I can't be the only one to have seen clouds of (recondensed) water vapour rising from wet roads when the sun comes out from behind clouds. Seen it happen all over the world, and I'd be surprised if Dixieland hasn't seen it too. No, it may not be steam, but it's what everyone calls it. They don't say ''Look at that cloud of recondensed water vapour''! In this respect, even horses can give off ''steam''!

[TCL-MUMPING]

Water may "steam" in the sun but I think if you were to hold a hand over that "steam" and then steam from a kettle, you'd appreciate the difference.