Hands-on science: Spud Missile
Spud Missile
Make your own super-easy and super-speedy spud gun.
Forget frying and roasting, the best thing to do with spuds has to be firing! Join Dr Yan as he makes one potato go a long way.
Step by step
Yan's video guide
In order to see this content you need to have both Javascript enabled and Flash installed. Visit BBC Webwise for full instructions
Join Dr Yan in making a super-easy and super-speedy spud gun.
Checklist
| Difficulty: low | Providing your copper tube is already cut down to size. |
| Time/effort: | You might need to buy some extra tatties. |
| Hazard level: medium | Careful when grinding the pipe into the potato. |
SAFETY: The spud gun can fire great distances at pretty high speeds. Make sure it is never pointed toward any people or animals. You will need a clear and open space when firing.
You need
A piece of copper piping
1 large potato (at least)
A metal nail file
A piece of dowel or a garden cane
A target, or perhaps a tree to act as a target
What you do
The copper pipe needs to be straight and smooth.
Take a piece of copper piping. You can buy this at your local DIY store and if you're lucky, they'll cut it down to the size you want. If they don't, ask someone who's experienced in sawing to help you out.
Check the copper pipe is straight and smooth
File down rough edges.
Carefully feel the sawn end of the pipe. If there are any rough edges file them down (a metal nail file works well).
Push the pipe into the spud.
Place a large potato on a table/bench. Steady it with one hand. With the other, push one end of the pipe into the spud, all the way through. One end of the pipe should now be sealed with a piece of potato.
Do the same with the other end of the copper pipe.
If you want to be like Yan, pour some pen ink (from a tub) into a plastic cup. Dip the firing end into the ink.
Line the pipe up and aim the smooth end toward your firing target.
Make sure there is nothing in your way - especially any people or animals!
To fire, poke the back piece of potato.
Grab the wooden dowel/garden cane and poke the back piece of potato.
Ready. Aim. Spuds!
If you're still dreaming about your spud gun experience when sitting at your desk, then read down the page and make your own desktop version.
What should happen
Ready. Aim. Spud!
The piece of potato at the front of your gun should fire out - with a great noise and even a touch of smoke - at an impressive speed. When it does, it should leave you with the overwhelming urge to do it again - and again. Just beware: there might not be any tatties left for dinner.
If it doesn't work for you
The pipe must be straight and smooth. Any dents will impact on how effective it is.
The edge where your pipe was cut also needs to be very smooth. If it's rough, file it down until it is completely smooth.
The front end of your spud gun needs to be clogged with the potato. Make sure you have pushed in enough spud to make it airtight.
Make sure you empty out the piece of potato still inside your pipe before setting up your next turn. Take the poker and jab at the potato inside. It will fall out the bottom – and make a very satisfying popping sound when it does.
Desktop spud gun
Make a spud gun mini-me
Warning: This activity requires the use of a saw. Children should be supervised.
Take an ordinary ball point pen.
Pull out the ends and the plastic ink column inside (you might need to use pliers). You should be left with an empty cylinder.
Saw both ends so they are equal in appearance and width. You can buy a mini saw for a few pounds in your local DIY store.
Take a nail file and file the rim of one end of the pen. Ensure it is smooth and that there is no rough bits leftover from the cutting.
Fill the tiny hole in the pen
If your ballpoint has a tiny hole in the middle (see image), clog it up using sticky-tack and tape.
Grind one end of the pen into a potato and then twist it as you pull it out. You need a good centimetre of potato stuffed inside.
Do the same to the other end of the pen.
Use a long and narrow poker (ink cartridge or cake skewer) to push at the back piece of potato.
The front piece should fly out.
This will travel far and with quite an impact. So, while it's easy to make at a desk, we don’t actually advise firing this in an office or class room!
What's going on?
Are you feeling lucky, spud?
The spud gun worked so efficiently because it employed the power of pressure.
As the potato is jammed into both ends of the copper pipe, it creates an airtight seal. This traps a volume of air inside the pipe. So, by pushing one piece of potato along the tube, as we do with the dowel, the space between the two potato pieces reduces. This compresses the air inside the pipe and increases the pressure. The pressure continues to build as the air is compressed until the force exerted onto the potato at the front of the pipe is so great that it overcomes the friction that holds it in place.
The result is that a piece of potato accelerates out of the pipe at a speedy, and may we say, impressive, rate.
Beam me up Scottie
There have been designs based on the same principle as this spud gun, to fire projectiles into space. The prototype, called SHARP, compressed hydrogen to such a degree (using a methane oxygen explosion) that it forced the satellite (equivalent to our spud) up the barrel and into space. Sadly, this prototype is no longer in practise.
Swot fact
Spud guns are not just used for recreational spud firing. The basic spud gun design also powers glitter and confetti launchers often used at sporting events.
If the science of spud guns has got you curious, then check out Jem's article on fire pistons...
BBC iD
BBC iDBBC navigation
BBC links
BBC © 2014The BBC is not responsible for the content of external sites. Read more.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.
