Anonymous
Anonymous asked in Science & MathematicsPhysics · 9 years ago

# Sound... What is amplitude?

I'm wondering what is it that creates the amplitude of a sound wave?

I understand that as represented as a transverse wave the amplitude is the maximum value of the wave function but how does this translate into longitudinal waves? It makes sense to me that the shorter or further the distance between a high or low pressure pocket of air makes the difference between a higher or lower frequency sound but seeing as the frequency determines the pitch and the speed of sound is constant (depending on the medium) what is it that provides a softer or louder sound? I've read that the intensity or energy of the sound waves is what makes it louder or quieter but if sound is travelling at the same speed what property of the wave as it travels through air is the term intensity or energy referring to?

Relevance

"Sound... What is amplitude?"

That is a really good question, because there is a problem with the definition of the word amplidude.

Amplitude is the magnitude of change in the oscillating variable with each oscillation within an oscillating system. For example, sound waves in air are oscillations in atmospheric pressure and their amplitudes are proportional to the change in pressure during one oscillation. If a variable undergoes regular oscillations, and a graph of the system is drawn with the oscillating variable as the vertical axis and time as the horizontal axis, the amplitude is visually represented by the vertical distance between the extrema of the curve and the equilibrium value.

In older texts the phase is sometimes very confusingly called the amplitude.

Particle displacement is called particle amplitude.

A transverse wave has an amplitude.

Particle velocity has an amplitude.

Sound pressure or acoustic pressure has an amplitude.

Sound intensity or acoustic intensity has an amplitude.

Sound power has an amplitude.

Sound energy has an amplitude.

Every (audio) frequency has an amplitude.

Sound energy density has an amplitude.

Sound energy flux has an amplitude.

A pendulum has an amplitude.

So what is amplitude?

A "sound" has an amplitude.

A loud sound has a bigger amplitude than a soft sound.

Which amplitude is really meant?

Cheers ebs