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Asked by Madeline to Keegan on 3 May 2016.
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Keegan Cooke answered on 3 May 2016:
I’m so glad you asked! I recommend googling it (with adult supervision of course). You’ll be able to make one with PVC pipe, a BBQ ignition, some hair spray, and of course potatoes. (Again adult supervision is required, as these things can be dangerous)
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Comments
Clay commented on :
There are a couple ways.
I use a PVC pipe with one end sealed, a bicycle pump with a sports ball needle, a rubber stopper, and a potato cut to fit the open end of the PVC pipe (but not too tight).
I insert the needle into the stopper. (This often requires drilling a hole through the stopper since most are solid – this can be tricky at best and dangerous at most.)
I drill a hole in the PVC pipe just above the sealed end, and just smaller than the middle of the stopper.
I insert the stopper into the hole and the potato into the open end of the pipe.
Then I start pumping air into the pipe with the bicycle pump. When the pressure inside the pipe exceeds the friction that holds the potato in place, kaboom! You have launch.
This is similar to the way you can make a bottle rocket. I still use the bike pump, needle and rubber stopper. Then I make some sort of stand that will hold the stopper in place. I put water in a plastic bottle (0.5 liter works best), insert the stopper, turn it upside down, put it in the stand, and start pumping. Air compresses, but water does not. And as with the potato cannon, when the air pressure inside the bottle overcomes the friction holding the stopper in the bottle (and the bit of extra bit of downward pressure due to gravity and the weight of the water), kaboom! The bottle launches and the water spews everywhere. This is great fun on a hot summer day. I experiment with the amount of water in the bottle, and the size of the bottle. If the bicycle pump has a gauge on it, you can read how much pressure it took to launch the bottle with different amounts of water in it.
Another propellant you can use to make a potato cannon is vinegar and baking soda. Put the baking soda in the pipe, add the vinegar, quickly insert the potato and wait. You can experiment with the amount and proportions of vinegar and baking soda required to produce enough pressure to launch the potato. When vinegar and baking soda react, they produce carbon dioxide gas. Gas has a lower density than liquids and solids, and so requires a lot more volume for the same mass. As the gas expands in the pipe, the pressure builds, and eventually, kaboom! You have lift off.
It would be a LOT messier, but you might put diet Coke in the bottom of the pipe, add some Mentos, quickly put the potato in the tube, and wait for the launch.