A wire and rubber band contraption that is being wound up.
Do you like to prank your friends and family? Give this little contraption a go. It’s the perfect thing to make someone jump, without causing any harm.

You will need

  • Large paperclip
  • Rubber band
  • Keyring (just the circle)
  • Pliers
  • Heavy book
  • Paper and scissors (optional)

What to do

  1. Straighten out the paperclip, and then bend it into a rough C shape.
  2. A piece of wire, slightly bent.About one centimetre from each end of the C, bend the wire outwards using pliers to make a little hook.
  3. Small piece of bent wire with a rubber band stretched between the ends.Put the rubber band on the C, so it’s stretched from hook to hook. If you need to, adjust the paperclip so the rubber band is not loose. Then take the rubber band off.
  4. Rubber band wound half way onto a metal ring.Now, pretend your rubber band is a key and start putting it onto the keyring. Stop when you’re about ¾ of the way on, and the rubber band is still trapped between the two layers of metal.
  5. Rubber band partially fed through the links on a metal ring and pulled taught on a metal wire.Repeat the last step with the same rubber band, only stop when it’s just ¼ of the way on. Make sure the rubber band is flat between these two points. You should now have part of the elastic band running straight across the circle of the keyring.
  6. Put the rubber band back on the wire C and adjust it so the keyring is in the middle of the C.
  7. Rubber band wound tight with metal ring and stretched on a piece of wire.Slowly wind up the keyring so the rubber band gets twisted.
  8. Wound up rubber band gadget being placed under a book.When you think it’s wound tightly enough, put the contraption flat on a table. Hold it still with one hand while you cover it with a heavy book.
  9. Wait for someone to lift the book!


There is a strip of paper inserted through a keyring in the middle of a rubber and wire contraption.


If you want the contraption to be even more annoying, you can slip a strip of paper through the keyring. Cut the paper just the right length that it hits the wire every time the keyring spins around, and it’ll make a loud buzzing noise!

What’s happening?

This annoying little machine is pretty simple, but it’s sure to shock your friends and family.

Energy is stored in the twisted rubber band, but it can’t release when it’s under something heavy. As soon as the book is lifted, the rubber band starts to unwind, spinning the ring. When the ring taps the table, the contraption jumps up into the air.

If you’ve added a paper strip, it makes a tapping sound every time the paper hits the wire. But it’s happening really fast, much faster than you can count. At a certain speed, you can’t perceive the individual taps and instead hear something closer to a note. Faster and faster taps will produce higher and higher notes.

Finally, did you know the startle reflex is one of the fastest reactions humans have? It can take less than 40 milliseconds for someone to start blinking, and 100 milliseconds to move their head and shoulders. At the same time, adrenaline and other hormones are dumped into their bloodstream, dilating their pupils and raising their heart rate. In a brief moment they’re ready to flee, or fight!

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