a steep slope that is covered in fresh snow. You’d

have a much harder time standing on the same

slope covered in a fresh sheet of ice, and the

reason is all to do with friction.

Friction is basically resistance, or drag. Just as

we came across air resistance with Britain’s

Fastest Bike and the Human Powered Aircraft,

and water resistance with our Hydroplaning

Motorbike, what we are dealing with here is

resistance between two solid objects – friction.

Friction provides grip, which is what gave me

traction on the bike tyres in previous challenges.

Far less traction, remember, on water than

on solid ground. What friction also does is to

generate heat. Try rubbing your hands together.

Press them hard together and you can feel the

resistance. You can also feel the heat. The kinetic

energy (movement) is being transformed into,

among other things, heat and sound energy. It’s

the heat that we are most interested in, because

that has a direct bearing on why snow and ice

are slippery.

There have been a number of theories over the

years about exactly why ice is slippery. Some

scientists have suggested that the surface of a

sheet of ice is not under the same sort of pressure

as the frozen water within the ice, so it does not

bond in the same way, allowing ‘loose’ particles

on the surface. A more common theory is that

the pressure of your foot standing on the ice,

and the friction you cause when your foot tries

to grip the ice as you attempt to walk, melts the

very surface of the ice, creating a thin layer of

water between your foot and the ice.

Try rubbing your hands together again,

only this time wet them first. There is far

less resistance, far less friction, far less grip.

Your hands are slippery when wet, the water

providing lubrication. The ice beneath your

foot quickly re-freezes once you have walked

away – or fallen on your backside, at which

point your hands, your bottom and your heels

will all be trying to grip the ice, melting their

own little patches, and, well, you’re now in a

proper state, aren’t you?

The only good thing about falling over on ice

is that, if you take it nice and easy, you can

generally get back up again, or at least crawl

away until you can find somewhere to stand up

that isn’t covered in ice. Snow is a very different

kettle of fish. If you fall over in deep snow – not

just up-to-your-knees deep, but the kind of

right-over-your-head deep snow that you find

on a mountainside – you sink straight in. A

FROST AND FRICTION    213