What powers a pneumatic device?

A pneumatic device is powered by air pressure, which is the reason the choice of air pressure is correct. Pneumatic systems operate by compressing air and using that compressed air to create movement or power mechanical systems. This is fundamental in various applications, ranging from tools such as pneumatic drills to industrial machinery that relies on the efficiency and speed of air power.

The other options represent different methods of operation. Electricity powers electronic devices and offers the versatility of automation and digital control, but it does not drive pneumatic machinery specifically. Hydraulic fluid is used in hydraulic systems, relying on liquid pressure rather than air, while gravity involves a constant force that dictates movement but does not generate the necessary power for pneumatic operations. Each of these alternatives serves its specific function but does not align with the fundamental principle of how pneumatic devices operate.