Time to explore air pressure again! This is definitely one of my favorite topics, mostly because we get to do fun things like launch pieces of potato! This specific demonstration is a standard in my Mr. O Demo Shows at the Children’s Museum of Houston. You can definitely buy either the Potato Propulsion Pipe from our Fiddle Sticks Toys shop in the Children’s Museum Houston or you can build your own!
What You Need:
A piece of pipe – I would recommend a thin-walled pipe like the copper piping you can find at your local hardware store. They come pretty long, as you can see in the video, but they can be cut down to size
A wooden dowel that just barely fits into the pipe and is, ideally, a little longer than the pipe (also available at the hardware store)
A knife to cut the potato
What to Do:
Cut a 1/2″-3/4″ slice of potato
Wrap duct tape near one end of the dowel to create a handle. This is an important SAFETY measure, as jamming your hand into a metal pipe at a high rate of speed is a great way to cut yourself pretty deeply. In the video I used a towel for this purpose, but the tape is more permanent.
Push one end of your pipe through the potato slice so that you get a piece jammed into one end
Push the other end of the pipe through the potato slice
Aim AWAY from anyone or anything living. Again, safety before fun so you can have more fun later!
Use the dowel to push one piece of potato towards the other through the pipe very, very quickly.
When one piece of potato is pushed towards the second, you compress the air inside the pipe. Compressed air is the same thing as saying you increase the air pressure. Air (and other fluids) always want to travel from areas of high pressure (ex. inside the pipe) to areas of lower pressure (ex. outside the pipe). So, the air pushes the piece of potato away at a pretty high rate of speed!
Why doesn’t it work if you push it slowly? Well, the potato isn’t an air-tight seal. If you push slowly, the air can just slip around the edges of the potato and leak out instead of building up pressure. By push the potato through quickly, the air pressure behind the potato builds faster than it can leak around it.
How could you get the potato to go further? Would a longer or shorter pipe help? What about changing the size of the potato? Go try it out!
Two Important Notes:
First, make sure to use your dowel to clear any leftover potato from inside your pipe before you put it away
Second, if you want, you can substitute the tube part of some pens (the kind you can open at both ends) for the pipe and an unsharpened pencil for the wooden dowel