Sound is made of vibrations. A musical note is a uniform vibration. Waves with a greater amplitude have more energy, which makes them sound louder.
Every musical note or tone has in it harmonics or overtones which add to the richness of the sound, and producing the characteristics of different instruments.
Sound vibrations may be seen with an oscilloscope. You can also make the vibrations of a string visible by using a very long, thick string or wire.
Every object has a natural frequency at which it vibrates, which is known as its resonant frequency. When struck, it will vibrate at this frequency.
Vibrations can be made in a variety of ways. Plucked strings and struck objects vibrate to make a tone, and resonance in a tube can make a tone.
Tone and pitch are both aspects of the frequency of the note being heard. The tone is a single frequency, the pitch is a subjective perceived frequency.
Sound can be observed and/or visualized in Chladni figures, made when a violin bow is rubbed on the edge of a steel plate scattered with fine sand.
Sound can be reflected and refracted. Acoustics is basically the study of how sounds are changed in an environment as they reflect and refract in a space.
Sound from a moving source that is moving towards or away, relative to the listener, appears to change frequency, due to the principles of the Doppler effect.
Thunder is caused by air being heated along the lightning flash, causing an increase in pressure. The bang from more distant parts takes longer to arrive.
Sonic booms are caused when an aircraft or other object travels faster than the speed of sound in the atmosphere at the level at which it is flying.
Beats occur when two very similar waves move in and out of synchronization, either reinforcing each other or cancelling each other at different times.
The bang of a gun, a firework or a handclap are all caused by the sudden release of gas under pressure. The bang is the pressure wave reaching our ears.
Sound travels through all materials as compressions and rarefactions, although it travels through some materials better (and sometimes faster) than others.
Sound is most easily considered as a wave, but may also be thought of as a cyclic variation in pressure. The model we use does not change the sound's nature.
In 1640, Marin Mersenne established a reasonable estimate of the speed of sound in air, which he set at 320 metres per second. The usual value today is 330 m/s.
The velocity of sound can be measured and shown to vary with the transmission medium and also travelling faster when the temperature of the medium increases.
The intensity of sound can be measured in decibels. Sound above a certain intensity can cause temporary damage to the delicate parts of the ears, or deafness.