What you need:
- Piece of paper
We didn't have a long piece of paper handy so we cut 2 strips of A4, about 3cm wide. Then taped the short ends to make one long strip.
Then hold one end of the strip and give the rest a half twist and tape the two ends together (if you imagine the paper has a front and back, you tape the front to the back)
This will give you a loop.
Put the pen in one spot in the middle of the inside of the loop and draw a line through the middle, don't take the pen off the paper.
Magic! The pen has marked both sides of the paper!
How does it work?
What will happen if you cut along the line?
Does this trick have any practical applications?
For older kids you can get into the maths behind it all, it's a good springboard for many activities.
It is the same principle that they use in conveyer belts, audio tapes and typewriter ribbons (OK your kids might not know what they are, get some history of machines in there too!) because it uses both sides equally, so equal wear and tear.
More recently infinite scarves have been popular - same thing! So your speedy science experiment can now be a knitting project!