How To Make A Straw Stab A Potato

Is it possible to stab a potato with a drinking straw?

We bet you don’t know the answer.

But you can find out with this fun science project for kids that shows how air pressure can be used in surprising ways!

What you need:

Stiff plastic drinking straws (no bendy straws)
A raw potato (or two!)

How to do it:

Grab a good sized potato in one hand with your thumb and fingers (don’t put your hand behind the potato).
With the other hand, hold a plastic drinking straw by it sides (without covering the hole at the top) and try to stab the potato. What happens?
Now repeat the experiment with a new straw but this time place your thumb over the top, covering the hole. Did it make a difference?

Why it works:

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? Without your thumb covering the hole, the air is simply pushed out of the straw and the straw crumples and breaks as it hits the hard potato surface.

In your second attempt, by covering the top of the straw with your thumb you are trapping the air inside. This forces the air molecules to compress and give the straw strength, which in turn keeps the sides from bending as you stab the straw into the potato. This makes the straw strong enough to pierce the potato, unlike the first attempt where the straw more than likely bent or barely broke the surface.

For some extra fun:

Use different diameter straws. Are the bigger ones harder or easier to stab with? How about the small ones?
Try stabbing different vegetables and fruits to see how deep you can get your straws to go in. Keep a journal to see which are easiest (or hardest) to poke!