Understanding Mechanics – Waves.

A major subject brought up in physics discussions is wave mechanics. Unfortunately, physicists know very little about waves and almost nothing about mechanics therefore you cannot really expect anything sensible from their discussions.

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Waves are mainly divided into two groups.

Group A  is the transmission of energy. Normally travelling waves

Group B  Is the transmission of mass. Normally standing waves

Both groups are further divided into Generated waves and Created waves.

If you drop a pebble into a pond waves are created that transmit energy. They are created because the pebble does not have any ‘wavelike’ properties and the ‘falling’ motion does not have any ‘wavelike’ properties.

Generated Waves

Electrical/radio waves are generated. The waves in a ripple tank are generated. The large waves sometimes found in holiday swimming pools are generated.

Generated waves follow a ‘pattern’, like the electrical generator that may rotate at 50 revolutions per second will generate electrical waves at a frequency of 50 cycles per second. The pulse mechanism on the ripple tank will generate waves at the same frequency as the mechanism itself.

Created Waves.

Normal waves in the sea are created, and are caused by two different mechanisms.

A. Being caused by the winds operating over the oceans.

B. The tidal flow across the Earth.  (Note; the tidal bulge itself is  a generated wave, it follows the ‘pattern’ of the moon’s movement around the Earth.)

If there was no land-masses the tidal bulge would flow smoothly across the globe. However, due to the land masses. parts of the tidal bulge ( really a single wave travelling around the Earth) are reflected from the land creating waves which are transmitted back into the seas. (This wave creation normally requires a vertical face to reflect from to create serious waves.)

Tsunamis are created, and may be considered in the same way as dropping a pebble in a pond, in that  they may be caused by a landslip (massive pebble). Tsunamis may be caused by a sub-sea  earth-quake or volcano, but the mechanics involved is the same as dropping a pebble in a pond.

However, when a tsunami hits the shoreline the transmission of energy changes to a transmission of mass. All the energy stored in the tsunami is transferred into moving the mass of water onto the land. If the tsunami hits a vertical rock face then a wave is created that is reflected back across the ocean

Ripples on the Beach.

These should be considered as created waves. They are formed due to the water rushing up the beach picking up sand particles. As the amount of sand in the water increases, the extra weight slows the speed of the water and the sand begins to fall out again. This pick up and drop out creates the ripples. The same thing happens as the water retreats down the beach and the ripples are changed again.

Neither the sand nor the water surge up the beach have any wave-like properties

Waves and Ripples in the Desert.

Caused in the same way as ripples on the beach, but by the wind instead of water. The huge dunes seen in deserts are the ‘sand breakers’, the equivalent to the sea breakers beloved by surfers. The wind speeds in the deserts are higher than the water speeds in the sea.

Neither the sand nor the wind has any wave-like properties.

Neither of the above two are really waves, but ‘wave-forms’. True waves must transmit mass or energy.

Obstruction in Smooth Flow.

If you have a smooth flow of water and you poke a stick into the water, then waves/ripples are created in the water just in front of the stick and pass each side of the stick.

It is clear that neither the water nor the stick have any wave-like properties.

In this situation there are three distinct actions occurring.

A. Below the surface of the waveform itself  there is an increased flow of water (mass) along the waveform.

B. The surface water flow passes over this flow. (If you drop a light object such as a petal onto the water surface upstream of the stick, the petal will cross over the waveform without deviating.)

C. As the waveform travels downstream it also moves sideways, (as a boats wake does). This indicates that there is also a transfer of energy sideways. (This is caused by slumping of the waveforms)

(In water waves you also have to allow for differences in speed between the surface water and the various sub-surface levels.)

Sorry about this , but fluid mechanics are extremely complicated, and light follows the laws of fluid mechanics.

Accelerating Waves.

See also ‘Introduction to Physics’. Click on tab at top of page.

Brian Williams – Author