Invisible Pressure Waves Around You

Right now, every sound you hear is actually air being repeatedly squeezed and stretched. When someone speaks, their vocal cords vibrate, pushing air molecules together (compressions) and apart (rarefactions). This ripple of pressure differences travels outward at 330 m/s and enters your ear canal, vibrating your eardrum — and your brain interprets that vibration as sound. Bats navigate by sending out ultrasound pulses and listening for the echoes bouncing back from insects and walls. Doctors use the same principle with ultrasound scanners to see inside your body without any surgery!