How Dangerous is Your Christmas – 2. A Scientific Christmas Party

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!

Festive experimentation with balloons and Christmas crackers.

Activity 1: Balloon kebabs

Is it possible to push a sharp kebab stick through a balloon? Of course it is! But you need to know the technique...

You will need:

  • Balloons
  • Wooden kebab sticks
  • Margarine or butter

Blow up your balloon – not too much – and tie the end. Look for the dark patches near the tied end and at the top of the balloon. The rubber is not as stretched there, and it’s those dark patches you want to try to push your skewer through, in one end and out the other. Twisting the stick will help as well. It’s a good idea to dunk the kebab skewer into a little bit of margarine before trying as well. This will act as a seal and prevent all the air from escaping quite so quickly as you push the stick through.

What’s happening?

Rubber is a polymer – it’s made of long chain molecules, a bit like a plate of spaghetti. When you blow the balloon up, they get stretched out. Where there is less tension, where the balloon’s surface is less stretched out, it’s easier to push the stick through the strands of rubber. On the stretched sides, the skewer is more likely to break them, and the balloon will burst. Have a try yourself!

Activity 2: Static electricity

Try rubbing some blown up balloons on a soft jumper, or your hair – does it make your hair stand on end? This is the effect of static electricity. As you rub the balloon, you are giving it a negative electrical charge. Now try making the balloon stick to a wall, or the ceiling if you can reach. As you move the balloon near to the wall, the surface of the wall becomes positively charged – because opposites attract – and so the balloon sticks to the wall.

In the programme, Fran Scott and Dave Porter go one stage further in doing tricks with static electricity. Instead of a balloon, they use a length of PVC pipe from a DIY store, and rubbed that on jumper. They then had six strands of very thin tinsel, about 1mm wide and 15 cm long, tied together at both ends. When the tinsel was touched to the charged pipe, it picked up the same negative charge. And because two things with the same charge repel each other, the tinsel forms an orb shape (because all the strands repel each other too) and floats above the pipe. But Dave’s tinsel was very light and came from a special science kit, so it may not work with normal strands of tinsel. If you do succeed, let us know!

Activity 3: Why do crackers go bang?

Have you ever taken a cracker apart and looked at the strip inside which is responsible for the bang? If you look at a cracker snap you’ll see that it’s made of two strips of card, bound together in the middle. The overlapping strips are coated with a chemical that’s similar to gunpowder! When you pull the cracker, the friction between the two bits of card as you pull generates heat, which leads to the BANG! A simple way to see how friction generates heat is just to rub your hands together.

You can buy cracker snaps in craft shops or online, and have a go at making your own.

You will need:

  • Cracker snaps
  • Wrapping paper
  • Cardboard tubes (eg toilet roll tubes)
  • Ribbon
  • Glue
  • Tape

Place your cardboard tube on the paper and cut the amount you need –Dick and Dom needed a length of about 18cm x 30cm, wide enough to wrap around their cardboard tube, and long enough to give ends you can pull.

To make the crackers easy to pull, you need to weaken the ends. Fold the paper about 3-4cm away from the cardboard tube, and cut out very small triangles along the fold, perforating the paper to make it easier to tear,

Next, attach your cracker snap, gluing or taping it down well to each side of the cracker. Then fill your cracker with whatever treats you want to go inside. Roll the paper around the tube, and tape it up. Lastly, tie the ends with ribbon to hide your perforations.

How Dangerous is Your Christmas