How Dangerous is Your Christmas – 4. Seasonal science

Scientists Dave Porter and Fran Scott show Dick and Dom some festive science experiments. If you would like to try them yourself, here’s how!

Instant ice, crawling through a Christmas card, and tuneful homemade instruments.

Activity 1: Instant Ice

For this activity you need 3 or 4 plastic bottles of still mineral water, in bottles which are as smooth as possible inside (no ridges or corners).

Put your bottles in the freezer. Every half hour, check whether they are frozen – but be very careful not to knock them. If you get to a point where one or more bottles has frozen, but the others haven’t, take them out of the freezer. Now, take a bottle that still has liquid water in, and give it a bang on the table. The water should turn to ice – instantly.

If all your bottles freeze, let them defrost and try again, checking more frequently.

What’s happening

The bottles of water are supercooled – they’ve been cooled below their freezing point of zero degrees Celsius. But it’s easier for water molecules to turn to ice crystals if there are already crystals there. If there’s nothing to start the process, the crystals don’t form. All it takes is a bang – and those crystals start growing, freezing the entire bottle.

Activity 2: How to crawl through a Christmas card

Do you think you could make a big enough hole in the middle of a Christmas card to fit your entire body through? Here’s how:–

Take some scissors, and at the fold of the card, make a shallow half-moon cut, leaving half a centimetre at the top and bottom of the spine intact, but cutting so there’s a thin hole in the middle of the card when you open it up.

Then starting at the spine, about half a centimetre in from one of the edges, cut across the card – leaving about half a centimetre from the very end. Next, from the opposite side, make a cut about half a centimetre from your first one, this time going towards the spine. As before, leave about half a centimetre from the end. You should now have two cuts going in opposite directions. Repeat these steps until you run out of card. You need to make sure that the last snip you make is in the same direction as your first snip.

Then fold it out... can you crawl through it now?

You can of course do this with paper if you don’t want to cut up any of your Christmas cards!

Activity 3: Straw squawkers and a glassware orchestra

Make some musical instruments from items you might have in your kitchen. In these activities, you will be making items vibrate so that they produce sound.

To make a squawking straw, you need a drinking straw, the wider the better. Flatten one end between your thumb and finger. Then snip off the corners of that end, so that you have a shape like a triangle with a flat top. It’s the two sides of this top that will vibrate together to produce the sound. To do that, you need to blow into it! You can change the pitch by making the straw shorter – try snipping off the end gradually, and listen to what happens.

You can also make sounds using wine glasses. Put some water into a wine glass. If you dip your finger in the wine glass and run it around the rim, pushing down gently, it should make a noise as it vibrates. You’ll also be able to see the water vibrating inside the glass. Experiment with different levels of water to change the notes – adding more water will make the glass heavier, and harder to vibrate, so the note will be lower. If you have access to a tuner and several glasses, you may even be able to work out how to play a tune.

How Dangerous is Your Christmas