Why does the metal pole on the DART feel colder than the seat?

If you put a finger on the metal pole on the DART and a finger on the fabric of the seat the metal feels colder. The temperature in the space you're in – indoors or outside – is probably pretty constant.

So why does the metal feel colder?

It has everything to do with atoms and how they’re bonded together.

Wood, glass, metal – all materials – are made from atoms, which are bound together like tennis balls attached to springs.

At low temperatures these 'springs' are rigid and the atoms don’t move about. As temperatures begin to rise the springs become looser. Heat is just what we call the energy that atoms in a material have to move about.

Caloric Theory

Scientist often make assumptions when they come up with concepts to explain phenomena.

They use experiments help to test these concepts, and if the experimental data doesn’t support their thinking, they come up with new concepts to test. This is how science advances. Occasionally, even ideas that later prove to be wrong can still be useful. Enter Caloric theory. In 1783 Antoine Lavoisier proposed a theory that heat was an actual substance that flowed from hot to cold areas. So, in our metal pole experiment, heat particles would be flowing out of you in to the pole. Caloric theory did a good job of explaining how a hot pot would cool, how air expands when heated, and was even used to develop heat engine theory – which was the basis of the mechanical engines that powered the industrial revolution. The effects that Caloric theory described were folded into thermodynamics, and these days we mostly remember the theory by its namesake, the calorie.

Different materials have springs that behave in different ways, making materials more or less efficient at transporting heat.

The springs that hold metal atoms together are really, really good at transporting heat. They're like motorways, where as the springs in wood are like a country laneway.

This is why different materials in the exact same environment can feel hotter or colder to us despite being at the same temperature. How we perceive temperature depends on how quickly we are losing heat.

Superconductors

Some tiny particles carry an electrical charge.

When these particles travel through a material they bump into atoms, causing resistance. The particles slow or stop, causing the material to heat up, which isn’t very useful. Metals are not just excellent conductors of heat, they’re also fantastic conductors of electricity. In metals, this charge can flow pretty freely with minimal resistance – it’s why we use copper in wires. However, an ideal conductor would be one where an electric charge could flow completely unimpeded. And these materials exist – we call them superconductors. When a superconductor is cooled to a very low temperatures it allows an electrical charge to pass with zero resistance – that means no loss, 100% efficiency. This is only the start of what superconductors can do. For example, at these low temperatures, superconductors also repel magnetic fields. If you place a superconductor over a magnet, it levitates.

If you touch the metal pole on the DART and hold your finger there for a few minutes, the point of contact will remain cool to touch.

If metal is so good at conducting heat, why doesn’t the heat of your finger make the pole warm?

Why does your tongue stick to the lamp post?

If you've ever been tricked into licking a lamp post on a freezing cold winter’s day, you'll be very familiar with how metal conducts heat. As your tongue touches the lamp post heat is very quickly transported away from the point of contact. Heat will continue to flow from your warm tongue to the cold pole until they reach a common temperature. Since the pole is far larger than your tongue, and far better at conducting heat, that final temperature will be very cold – maybe cold enough to freeze the water on your tongue, leaving you stuck to the lamp post. It should go without saying, please don’t try this. Just take our word for it.

It's the same principle at work.

Heat is being transferred from your finger, but it's spreading out through the metal's springs in a really efficient way. It's being carried away from the touch point so fast that we don’t notice any change in the temperature of the metal.