Difference between hydraulics & pneumatics?

Hydraulics deals with the use of liquid in motion, usually in a device such as a machine. Oil is the most common liquid used in pumps, lifts, and shock absorbers.

Whereas hydraulics uses liquids to achieve mechanical advantage, pneumatics uses compressed gas. Since gases can be compressed and stored under pressure, releasing compressed air can provide large forces and torque for machines such as pneumatic drills, hammers, wrenches, and jackhammers.