When you touch an object and it feels warm
or cold, what is that really telling you about the object? Here, I have a metal hard drive
and a book and I’m going to ask people to compare their temperatures. Which one do you
think will feel warmer – the book or the hard drive? The temperatures? Yeah, tell me if one is hotter or colder or
if they’re the same temperature. How do they feel? This is slightly cooler than this one. Oh, that’s warmer. Yeah, agreed. I’d say the hard drive is a lot colder than
the book. ‘Cause the book’s got more knowledge. Why do you think that is? Metal’s normally a little bit chillier if
you leave it in a colder temperature. What if I said they’re both the same temperature?
What would you say? I’d tell you you’re lying. I’d think you were lying, yeah. Well, maybe the way I can prove it is I have
an infrared thermometer. What do you think we’re going to see? I think science might be able to answer that.
And I’m not a scientist! Make a prediction for me. I still think that’s colder. Would you bet me money? I don’t have any cash. Let’s measure the temperature of the book.
What do you see? 19.0. OK. Now measure the temperature of that. 19.0. Alright, well, now I believe you. I’m trying to figure it out, actually. Trying
to figure out why’d they be the same temperature. They don’t feel the same temperature, though. So, why does that feel colder if they’re the
same? Good one. You know the answer? I’m coming to you guys for answers. We’re creatives, not intellectuals. Well, create an answer for me! I’m not a scientist! Come on, you tell me. I’ll try to answer that question with another
little experiment. Here is an aluminium block. Ooh! Nice and cold. And a plastic block. How do their temperatures
compare? Completely different. Aluminium’s going to be much colder. Yeah? This actually feels colder. Let’s take this to the next level. I’ll put
an ice cube on both plates. What will we see? I’m guessing it would stay solid on this one
and melt on this one. So it’s going to melt on the plastic but stay
solid on the aluminium? Yes, but maybe I’m wrong. That one will melt more quickly than on the
aluminium. You’d think so. Yeah, ’cause it’s cold. I think they’re the same. We put an ice cube on each of those. What
do you see? It’s melting quicker on the aluminium. My God, it’s melting! This is melting quicker than that one, even
though this is aluminium and that’s plastic. So which one felt colder? This one. How does that make sense? No idea. Could aluminium be bad for the environment? How would aluminium be bad for the environment? It’s thawing the ice quicker, isn’t it? You want the answer? Yes, please! It’s about thermoconductivity – the rate at
which heat is transferred from one object to another. So when you felt these blocks
originally, I know this one felt a lot colder. But you know from the other example we did,
that they must both be the same temperature. True. They’ve both been outside for a while. We
see the aluminium block is melting the ice faster than the plastic block because it’s
conducting the heat to the ice cube faster. With the plastic block, it’s a worse thermoconductor.
So, heat is being transferred less quickly to this ice block and so it’s staying iced. OK. I believe you. Make sense? Yes. Definitely. In our first example, the hard drive felt
colder, even though it was at the same temperature as the book. That’s because the aluminium
conducts heat away from your hand faster than the book conducts heat away from your hand. Sure. That seems logical. Which makes the hard drive feel colder and
the book feel warmer. So when you touch something, you don’t actually feel temperature. You feel
the rate at which heat is conducted, either towards or away from you. Think about this
next time you hop out of the shower in winter. It’s much nicer to stand on the bath mat than
on a towel beside it. Not because the bath mat is warmer but because it conducts heat
less quickly away from you.