For our Energy Systems class, the prof wants us to do a project.  It can be basically anything that is relatively safe and not illegal, and deals with energy conversions (potential to kinetic, kinetic to electric or mechanical, etc).  Our group was thinking about an advanced potato launcher, but I'm sure there are some better ideas out there.  Something explosions/firearms related, hopefully.  So if you have any good ideas, let me hear 'em.

Spud Gun (chemical to kenetic) - already mentioned.
Flame Thrower (chemical to heat)
muzzle energy from rifles (chemical to kenetic)
rail gun (electric to kenetic)
catapult (mechanical to kenetic)

tannerite - though I don't know how you would get useful work

rail gun.

a lightweight go cart powered by multiple large fire extinguishers.

Build a giant ballista.

It's like a crossbow, but meaner.

A moped made out of a mountain bike and a chainsaw.

Trebuchet - potential to kinetic

Welll...how about a hemp burning machine

Back in eng. school, one of my stand-by projects was to put a warhead on a model rocket....

Could do it with like m60s or black cats...

Didn't have the time or $$ to develop a guidance package though...

I'd vote for pnuematic spud gun (potential to kinetic),  because it is easy to model and easy to build to prove out the model if required.  And things that shoot 'r fun!!

Kent (mechanical eng.)

Watch the music video for "An Honest Mistake" by The Bravery.  4 Minutes of Rube Goldberg Machine that should provide some good ideas.




Hold a firecracker in your hand and a lighter in the other.  Chemical Energy
Light Firecracker, continue to hold.
When it explodes you will have demonstrated chemical energy to mechanical energy.
The mechanical energy will transfer to you hand and cause a hurting sensation in your brain. Mechanical to Chemical

As an automatic nervous system response you will exhale sharply - Chemical to mechanical energy
The air you exhale will pass over your vocal cords, and cause them to vibrate in a most curious fashion FUU@@####!!!!  Mechanical to Mechanical

If you can borrow an oscilloscope and a microphone you can capture the waveform that you just produced - Mechanical to electrical

The professor will walk over and slap you for swearing.  The female engineer in the second row that you thought you had a chance with will laugh in derision.

Elizabeth: Paul, did you build an atomic bomb?
Paul: Only a little one.

Remote wireless power.
Can you fire a laser accross a canyon/classroom and power a light bulb with a simple solar panel?

Let us know

Thanks for the ideas so far.  I had actually been thinking something like a ballista/catapult/trebuchet.  Rail gun was one of the things we all mentioned, but I don't know about actually building one.  The flamethrower is a good one I haven't thought of, though I'm not sure how the prof will receive that one