What you'll need:
- Stiff plastic drinking straws
- A raw potato
- Hold a plastic drinking straw by it sides (without covering the hole at the top) and try quickly stabbing the potato, what happens?
- Repeat the experiment with a new straw but this time place your thumb over the top, covering the hole.
Placing your thumb over the hole at the top of the straw improves your ability to pierce the potato skin and push the straw deep into the potato. The first time you tried the experiment you may have only pierced the potato a small amount, so why are you more successful on the second attempt?
Covering the top of the straw with your thumb traps the air inside, forcing it to compress as you stab the straw through the potato skin. This makes the straw strong enough to pierce the potato, unlike the first attempt where the air is pushed out of the straw.