1I s it possible to walk across the English Channel? 21
It would be – if it was frozen. But will this ever happen? We all know pure water freezes at 0 ºC. But salty water doesn’t freeze until it gets even colder. There is a lot of water in the channel. It would take ages for all the particles to get into a regular pattern and form ice. So it would need to be very cold for a very long time to freeze the channel.
Grit is actually rock salt - a mixture of crushed rock and salt. It’s what they dig out of salt mines. So why use salt? Salt can stop water freezing. When the salt dissolves, it lowers water’s freezing point. So ice will only form at temperatures much lower than 0°C.
3 It's 4 o C today, so how come the snow hasn’t melted?
Melting takes time. It’s the same with ice-cream. Why? The ice particles have to absorb energy to overcome the attractive forces holding them together. Supplying enough energy takes time.
4 The road is ice-free… … but in 10s the driver will skid over the side of a bridge! Why?
Bridges get icy (and slippery) before the roads on land. Why is this? Bridges contain a lot of metal, so they cool down quicker than roads. Bridges lose heat fast because metals are such good conductors.
5When can water pack a bigger punch than a boxer?
Water forms ice when it freezes. But why is ice so hard? Look at these icicles, you wouldn’t want one falling on your head! Icicles are hard because strong forces hold their particles together.
6Why might cold spells give joy to children at Christmas?
Sprouts contain water, so what happens when the temperature drops? The ice in frozen sprouts is brittle. It shatters in the machines that harvest them, which breaks the sprouts up. Frozen sprouts can be harvested by hand, but this is slow and expensive. So lots of children will have to go without sprouts on Christmas Day.
If you stayed out in freezing weather for too long, you would die. But wood frogs can survive. How? They fill their cells with sugar. This acts like antifreeze to stop them freezing solid. The frog’s antifreeze stops ice forming the same way salt stops it forming on roads.
8 You throw water up - snow comes down. How come?
The air has to be cold – very cold. In Siberia it is –40 ºC. What happens to the water in the air? It freezes instantly as water particles lose energy and fit together to form crystals. Throwing it up helps by forming droplets. Their large surface area, makes them lose energy faster.
liquid water solid water 9 Why is water strange?
If this was any other substance, the solid state would sink. So why do icebergs float? When most substances freeze, their particles get closer together, so they get denser. Water is strange because the particles in ice crystals are more spread out, which makes it less dense than water.
10Santa has a new sledge. It’s made of plastic. Is this a good choice of material? 21
Plastic is lightweight so it’s easier for his reindeer to pull, but will it survive the freezing temperatures on Christmas Eve? Maybe not! Plastic particles are like strands of cooked spaghetti. They slip and slide over each other to make a soft, flexible material. But when the temperature drops the particles lose energy and stick together. The plastic goes rigid and brittle like glass. Any small pushing force could make the sledge shatter.