HowDoWhy

 I’ve always been a bit of a science nerd so when, many years ago, a girlfriend insisted that cold water would boil faster than hot water, I refused to simply take her at her word. First I applied some critical thinking - a step I highly recommend whenever somebody tells you something that sounds a little off.

Boiling water is simply approaching a transition state between one form and another. It is in a liquid state and approaching a gas state. In order for any material to change states you either have to increase or decrease energy. Basically, you’re trying to excite or calm the molecules in the material.

In the case of water, its normal “room temperature” state is as a liquid. Remove heat (energy) sufficiently and it will become a solid (ice). Increase heat (energy) sufficiently and it will become a gas (water vapor or steam).

Now, and here’s where my science breaks down a bit, if I want to boil water, I have to excite those molecules. I have to get them moving. A passing familiarity with the laws of motion had me thinking that it’s easier to move a boulder already in motion than it is to move a boulder that’s standing completely still. It takes less energy to move or maintain motion in something that is already in motion. Seems that would apply at the molecular level too, wouldn’t it?

If you accept that you need energy to “move” water molecules sufficiently to boil water and you also accept that the molecules in cold water are moving slower than the molecules in hot water, common sense would dictate this myth is false. The same amount of energy applied to the same amount of cold water vs. hot water should result in reaching the boiling point more slowly. It also stands to reason that a pot of water just short of boiling is going to get there a lot sooner than a pot of water pulled from the freezer just before it freezes.

So there’s the common sense approach of applying logic. The actual experiment was pretty simple. Let the faucet run on cold, fill a pot with two cups of cold water and time how long it takes to boil. Then repeat but use water from a hot tap. In an effort to inspire your own scientific interest, I’ll leave it to you to try out but I’ll give you one big hint on the results. The myth was wrong.