Verified answer

look up the "triple point"of water this is the temp at which water can exist at all three states(gas,liquid,and solid)depending on the pressure it is under

First: Atmospheric pressure DECREASES the higher you go.

Second: It is correct, that decreasing atmospheric pressure leads to a lower boiling temperature the higher you get. That is because the water molecules have less pressure to fight against before becoming vapor (i.e. boiling). Therefore, they can boil at lower temperatures. This is easier to understand if you think of the pressure being related to the weight of all the air above you. The higher you go, there is less air above you, therefore it weighs less and the pressure is less.

The reason that it takes longer to cook at a lower boiling point is because the temperature is lower. The lower temperature means that you must wait longer for the food to heat enought to be cooked.

You are correct in thinking that water would boil quicker at a higher elevation due to the lower temperature required. However, boiling water at 98°C is not as hot as boiling water at 100°C -- so you still must cook longer.

There is a fascinating flip side to this!

You now know that water boils at low temperatures when the pressure is low.

If you ever see a fountain on a really warm hot summer day..... you can put your hand deep underwater and try to move it really fast. The result will be that behind your hand builds an area of low pressure BEHIND your hand - a sort of "vacuum". If you push your hand fast under water enough you will see small vapor bubbles forming. This is not air, but believe it or not -- that is water BOILING --- but at a temperature of only 100°F/40°C --- this is because of the very low pressure of your hand is creating allowing the warm molecules to easily turn to vapor!!!!!

(However, don't try to cook an egg behind your hand. 40°C is still 40°C and the egg will never be cooked!!)

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If pressure decreased 1 bar every 10m up from sea level, this would result in a total vacuum at 10m altitude. This isn't the case.

Air pressure is approximately half a bar at 17000 ft.

Boiling point decreases with decreasing ambient pressure. The water will boil more quickly, but will not be hot enough to cook the food

The boiling point of water at 29000ft (Mt Everest) is 72 degrees C - you just can't make a decent cup of tea!

The opposite of this is the pressure cooker. The ambient pressure increases to 2 bar, the boling point is increase to 120 degrees C and the food cooks in fifteen minutes!