CONCEPT: The speed of sound through various substances varies.

Find out how waves work, and what the difference is between how a sound wave and a light wave travel.

A sound wave is a pressure disturbance that travels through a medium by means of particle-to-particle interaction. As one particle becomes disturbed, it exerts a force on the next adjacent particle, thus disturbing that particle from rest and transporting the energy through the medium.

Like any wave, the speed of a sound wave refers to how fast the disturbance is passed from particle to particle. While frequency refers to the number of vibrations that an individual particle makes per unit of time, speed refers to the distance that the disturbance travels per unit of time. Always be cautious to distinguish between the two often-confused quantities of speed (how fast…) and frequency (how often…).

Reference: http://www.physicsclassroom.com/class/sound/Lesson-2/The-Speed-of-Sound

Sound travels many times faster in some materials (for example: aluminium) compared with others (for example: air). Sound also travels a lot further in denser materials. In general, the higher the density of a material, the louder the sound.

On the other hand, sound intensity is significantly affected (usually reduced), when it changes from one medium to another (say when it travel from a solid into the air).

All other things being equal, the 'loudness' of a sound is directly proportional to its surface area - big drums are louder than little drums: A tuning fork emits a relatively feeble sound on its own, but when placed on a table, the particles of the table are forced to vibrate at the same frequency as the tuning fork: The table has a relatively large surface area and so the sound will become much louder.

The amount of energy that is transported past a given area of the medium per unit of time is known as the intensity of the sound wave. The greater the amplitude of vibrations of the particles of the medium, the greater the rate at which energy is transported through it, and the more intense that the sound wave is. Intensity is the energy/time/area; and since the energy/time ratio is equivalent to the quantity power, intensity is simply the power/area.

Typical units for expressing the intensity of a sound wave are Watts/meter2.

Reference: http://www.physicsclassroom.com/class/sound/Lesson-2/Intensity-and-the-Decibel-Scale

• Click to get full-screen version Sound interactive - experiment with musical instruments on-line
• A simple audio interactive to have fun with! Plink - Play some sounds - On-line jamming

CONCEPT: What is the difference between the loudness and pitch of a sound?

The pitch of the sound is the characteristic frequency of the the sound (measured in hertz) - the loudness is the amplitude or volume (measured in decibels).

The human ear is capable of detecting sound waves with a wide range of frequencies, ranging between approximately 20 Hz to 20 000 Hz.

The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high frequency sound wave and a low pitch sound corresponds to a low frequency sound wave. Amazingly, many people, especially those who have been musically trained, are capable of detecting a difference in frequency between two separate sounds that is as little as 2 Hz.

Humans are equipped with very sensitive ears capable of detecting sound waves of extremely low intensity.

Since the range of intensities that the human ear can detect is so large, the scale that is frequently used by physicists to measure intensity is a scale based on powers of 10. This type of scale is sometimes referred to as a logarithmic scale. The scale for measuring intensity is the decibel scale.

Reference: http://www.physicsclassroom.com/class/sound/Lesson-2/Intensity-and-the-Decibel-Scale