Hello Daisy,

I am sorry dear, but I am not sure I understood you. If your moist finger sticks to a very cold piece of metal, then it usually is because the cold makes the moisture freeze into ice, and the ice is like a glue that sticks your skin to the metal. This happens a bit when you take an ice tray out of the freezer with bare hands. (Be careful! If you do this too roughly it can pull off a bit of skin, and that is painful and can take a long time to heal! Explorers and other people who work in very cold climates, such as near the poles, have come to serious harm from touching cold metal, and I would not like the same thing to happen to you.)

But I am surprised if that could happen to your finger in a shower in England, especially if the shower was still working. If the cold tap stuck to your finger, the pipe should have frozen. And as for a hot tap... No!

Maybe I misunderstood you: did you mean that your finger felt cold when you touched the cold tap, and still felt cold even after you took it away? And that when you touched the hot tap you still felt the heat when you let it go?

If so dear, that is an excellent question and I hope you never stop noticing such things and wondering about them. It could change your life.

The problem is that a really full explanation is quite complicated, so I can only give you a vague answer, especially because I don't have any idea of what science you have learned so far. So I will do my best, but I hope that if anything I say doesn't make sense, you will come back and ask about the difficult bits, or the bits where I spoke nonsense. Right?

The first idea to bear in mind is that cold is not a stuff, it is a shortage of heat. Does that make sense? Where something is cold it is because heat has been taken away. It is like where you dig a hole in the ground and pile the earth to one side. The pile is where there is a lot of earth, but the hole is just the place where earth was taken away. I can give you a kilogramme of earth, but I cannot give you a kilogramme of hole, right? In much the same way, a hot tap can heat your finger by giving it some heat, but a cold tap can only cool your finger by taking away heat. We say that the hot or cold tap conducts heat into or away from your finger.

But as soon as your finger has lost some heat, it cannot get it back until more heat has been conducted back in, so you will find a cold patch there for quite a while. This is no surprise, because you know that if you put one hand in cold water for a minute or so, and the other in warm water, then dry your hands, you will find that the cold hand stays colder than the warm hand for some time, and the warm hand stays warmer, as you can check by putting your hands against your face to feel how different they are. It takes time for heat to conduct into your hand and it takes time for heat to conduct out of your hand.

Is that what you meant by cold “sticking to you”?

Now, I will stop here for now, except for just one warning. For many hundreds of years people thought that heat was a “stuff” like water or air, but a special kind of stuff that could flow through even solid metal. You can see why they thought that; it is a tricky business. I will not go into what it is if it is not a “stuff”. Instead, if you want to take this further, put in another question, if that is what you like, or if I simply have misunderstood, tell me what you really wanted to know,

All the best,

Jon