A vibrating source pushes on the air, squashing particles into a compression, then pulling back to leave a rarefaction where they spread out. These compressions and rarefactions race outward as a longitudinal wave, while each particle just shuffles back and forth on the spot. A compression is a squeeze of high pressure; a rarefaction is a stretch of low pressure. The pressure graph below tracks them.
MissionWatch the compressions travel, then judge where the pressure is highest.Streak 0Best 0
A compression, where the particles are bunched, is a region of:
compressionparticles bunched, high pressure
rarefactionparticles spread, low pressure
the wave travels right; each particle only vibrates back and forth on the spot.