Cutting Steel with Water

The power of water pressure (20,000-55,000 psi) and high speed (900+ mph):

http://science.howstuffworks.com/question553.htm

Digging with Air

An amazing new tool that digs a trench using compressed air:

http://www.savatree.com/airspade.html

It blasts the dirt with 1000+ psi of pressure -- enough to penetrate even clay.