What do we call the wall of pressurized air that builds up in front of fast-moving objects?

Ultrasound.
Sonic Boom.
Natural Frequency.
Sound Barrier.

In a system, when potential energy decreases, then entropy also decreases. true false

Air initially at 0.75 bar, 1000 k, and occupying a volume of 0.12 m^3 undergoes two processes. process 1-2: the air is compressed isothermally until the volume is halved. process 2-3: the air undergoes a constant pressure process until the volume is halved again. assume ideal gas behavior. a) determine the mass of the air, in kg. b) the work and the heat transfer for each of the two processes, in kj. (100 kj = 1 bar . m^3)

Which accurately compares concave and convex lenses?