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### 4.2 Understanding Basic Terms of waves

Waves motion changes both in space and time. Let us take the following image of the water wave from sideways at any given time, 123RF.com

In order to understand the basic terminologies, we compare it with the following (displacement-distance plot) of the wave above,

All we did was approximated a water wave to a trigonometric $sin$ function, and it does have a very close match with that of actual water wave.

*Note the black dot labeled in the plot above (that's just to label one of the water molecule oscillating up and down about the mean position). That particular oscillation motion of the water molecule has it own plot which looks similar to the wave plot above except that we plot the displacement with respect to time, which looks as follows,

So, there are certain terms in wavemotion that we'll need to understand. These are as follows,

Wavelengths: The wavelength is the distance between two consecutive points in the wave that are at the same stage of oscillation.

Displacement: The displacement is the difference between the distance of the mediums particle and its equilibrium value.

Amplitude: The amplitude is the maximum magnitude of the displacement.

Period: The period of the oscillation is the time taken for one complete oscillation. It is denoted by $T$.

Frequency: Frequency is the no. of complete oscillations per unit time. Its SI unit is Hertz($Hz$) or $s^{-1}$.

Here's the plot labelled with their basic terminologies. Make sure you understand the notion of wavelength and time period in context to wave motion clearly.

In addition, here's an informative video on wave motion in 5 part series, make sure you watch all the parts.