Boiling Water in a Paper Cup?

Were humans able to boil water before we discovered how to make metal cookware? Absolutely. We've been boiling water in large, cup-shaped leaves for thousands of years! We’re able to pull this off because of a process called conduction, whereby heat is conducted away from the leaf and into the water. Do you think it’s possible to accomplish the same thing with a paper cup?

It is very easy to boil water in a paper cup. It may not be a practical way to boil water, but it's a great way to teach kids (and maybe yourself) a few things, like:

1. You can't always predict the outcome of a situation based upon intuition. Paper should always burn when exposed to fire, and the outside of the cup is dry, so why doesn't it burn?

2. You can boil water in almost anything that will contain it, so the story about aborigines dropping hot rocks in a wooden cup to boil water is true.

3. There are things you can do in the home that will teach you science without destroying your kitchen.

How to do it:

• Step 1 - take a simple paper cup - it won't work with an insulated or double-walled cup, or a waxed paper cup, or two nested cups. Just abog standard paper dixie cup.
• Step 2 - Fill the cup with water (only water.) If you want to make tea, get a bag ready.
• Step 3 - Put it on the stove. If you have electric burners instead of gas, you need to trim the paper ridge at the bottom of the cup so that the surface of the cup rests against the metal.
• Step 3 - Heat. Soon the water will boil.
• Step 4 - Add tea bag if desired.

Why it works:

The water acts as a heatsink, removing the heat of the flame (or hot plate) from the paper, keeping the temperature below the ignition point. Paper burns at more than twice the temperature water boils. As long as there is water in the cup, it will not burn. Water boils at 100 C and paper burns somewhere in the ballpark of 200 C.  You could certainly heat the paper to 100 C and the water would boil without burning the paper.  If you put a direct flame to the cup, you should also be ok, so long as the paper is thin and the part of the paper cup touching flame is also touching water.  This is because objects in contact tend to equalize their temperature.  Water boils at 100 C, and it stays at 100 C as you add extra heat to it--you only change the rate at which is boils.  This means the paper touching it wants to stay at 100 C as well and it transfers any extra heat to the boiling water in order to do so.  So if you apply a direct flame to the bottom of a paper cup filled with water, the paper shouldn't burn.  Of course if the paper is thick so that it can't transfer the heat from the outside to the water quickly enough or if the water boils off, then the paper can burn.