Sound

Temperature, Humidity

Speed of sound increases with temperature (v ∝ √T) and humidity (moist air is less dense). At constant temperature, pressure doesn't affect sound speed in ideal gases. Frequency and amplitude don't affect wave speed in a given medium.

17 m

For distinct echo, the time interval should be at least 0.1 s (persistence of sound in brain). At 22°C, v = 344 m/s. Distance for echo = (v × t)/2 = (344 × 0.1)/2 = 17.2 m ≈ 17 m.

Particles vibrate parallel to wave direction, Can travel through solids, liquids, and gases, Cannot be polarized

Longitudinal waves have particle vibrations parallel to wave propagation, can travel through all material media, and cannot be polarized. They have compressions and rarefactions (not crests/troughs) and need a medium to travel.

Kinetic energy of air molecules increases

Speed of sound v ∝ √T. As temperature increases, kinetic energy of air molecules increases, making them move faster and transmit sound waves more quickly through the medium.