Ultrasonic waves have frequencies above the upper limit of human hearing, typically above 20 kHz.

Bats use ultrasonic waves (high-frequency sound beyond human hearing) for echolocation to detect objects.

Beat frequency equals the absolute difference between the two frequencies producing the beats.

Auditory persistence is typically about 0.2 seconds, so the sensation of a brief sound lasts roughly 0.2 s in the brain.

Each 1°C rise gives 0.61 m/s increase, so a 2°C rise gives 2 × 0.61 = 1.22 m/s increase.

For an ideal gas at a given temperature, speed of sound depends primarily on temperature (and gas composition), not on pressure; hence pressure is the independent factor here.

Air cannot support shear stresses (no modulus of rigidity), so only longitudinal (compressional) waves can propagate in air.

Beats arise from interference between two sound waves of nearly equal frequency causing periodic amplitude variation.

The Doppler effect (Doppler's law) describes the apparent change in frequency due to relative motion of source and observer.

The Doppler effect describes the change in observed frequency due to relative motion between source and observer.