Brighten up those dull winter days with Sophie Duncan's class conundrums.
December is a good time for some science party tricks. How much science can you do with a glass of water, a sheet of card and a handkerchief? Here are a couple of ideas to get you started.
Dampen the handkerchief. Take the glass and fill it three quarters full of water. Pull the handkerchief down over the top, securing it in place with an elastic band so that it is taut. Then push the handkerchief into the water using your finger and turn the glass upside down. The water will remain in the glass. Now remove your finger and pull the handkerchief taut again. You should find that the water looks as if it is boiling as bubbles rise to the surface. This happens because when you remove your finger the air pressure inside the glass is less than that outside, causing air to be drawn through the fabric of the handkerchief.
Take a seasonal-looking postcard. Ask your students to guess whether you can step through it. Hopefully they will say it is impossible. (If you feel confident you could cut the postcard in half, or even into quarters and still get this trick to work.) Fold the card in half lengthways. Using scissors, cut from the fold, stopping 0.25cm from the edge of the card. Do this at least fifteen times (the smaller the card, the more times you have to do it) making sure the cuts are equal distances apart. Cutting from the edge opposite the fold, cut in between the cuts you have already made, again stopping 0.25cm from the fold. With the fold at the top, turn down a flap at each end of the card. Now cut along the rest of the fold, making sure you do not cut through the two flaps you have turned down. When you open this card you will have a huge loop you will be able to step through.
Sophie Duncan is project manager for science at the BBC.