Pitch is the subjective perception of frequency; higher frequency results in a higher pitch.

An echo is a repetition of sound caused by the reflection of sound waves from a reflecting surface.

To hear a distinct echo, the reflected sound must reach the ear at least 0.1 seconds after the original sound. Given the speed of sound is 344 m/s, the distance must be at least 17.2 meters.

Ultrasonic waves have frequencies higher than the upper limit of human hearing, which is 20,000 Hz.

Ultrasound is widely used in medical imaging (sonography) to visualize internal body structures.

In a longitudinal wave, the particles of the medium oscillate parallel to the direction of wave propagation.

The loudness of a sound is directly related to the amplitude of the wave; larger amplitude results in a louder sound.

Sound travels faster in denser media (like water) compared to less dense media (like air) because molecules are more closely packed.

SONAR (Sound Navigation and Ranging) uses the echo of ultrasonic waves to determine the depth and map the ocean floor.

The speed of sound depends on the medium's elasticity (resistance to deformation) and its density. Generally, sound travels faster in denser and more elastic media.

Sound waves require particles to collide for propagation. Since solids like steel are more tightly packed than liquids or gases, sound travels significantly faster through them.

The Decibel (dB) is the standard unit used to measure the intensity level or loudness of a sound.

Sound requires a medium (like air, water, or solid) to propagate. As the Moon is a vacuum without an atmosphere, sound cannot travel there.

The Doppler Effect describes the change in frequency of a wave in relation to an observer who is moving relative to the wave source.

The audible frequency range for a healthy human ear is typically between 20 Hz and 20,000 Hz.

Persistence of hearing in humans is about 0.1 seconds. If the reflected sound reaches the ear within this time, it overlaps with the original sound.

Frequency is determined by the source of the sound and does not change as the wave travels through different media, whereas speed and wavelength do.

Infrasonic waves are low-frequency sounds below the human audible range of 20 Hz.

Timbre allows us to distinguish between two sounds of the same pitch and loudness, primarily caused by the combination of different overtones or harmonics.