IDC: Dive Theory Physics 2. Water, heat, light and sound

As promissed here is more Physics for you to use during your study time for the IDC.

Today we will be talking about water and heat, light and sound.

Water & Heat

Water removes body heat quicker than air
Water conducts heat from our body 20 x faster
Water is 770 times denser than air

Heat Transmission

Conduction (heat removal via direct contact)
Convection (heat removal via fluids)
Radiation (heat removal via electromagnetic waves) think about your heater in your room

Divers are mostly affected by Conduction

Water & Light

 Apsorption: :Colors are absorbed by depth starting in the rainbow order: red, orange, yellow, green and violet. . Even water at 5ft depth will have a noticeable loss of red. For this reason, strobes are usually used to add color back to subjects.

Fluorescents retain color underwater because their wavelengths are not common and they emit color when stimulated by light of any shorter wavelength. Fluorescence is a different extremely exciting color phenomenon. If a fluorescent color is illuminated by light electrons start to swing and the color glows – but different. UVA light is invisible for us but lets the fluorescent colors illuminate in their true colors! The big difference between fluorescence and normal colors is the “glow effect”, which makes invisible light visible.

Diffusion: Scattering of light (prevents light reaching a certain depth)refraction-by-Moh_Tj-on-flickr

Refraction: Apparent size & closeness is affected by refraction
Light bends as it passes from air to water, due to water being more dense, therefore light slows in speed. Objects appear closer by ratio of 4:3 (an object 4 meters, will appear 3 meters away)

Size Refraction causes the size of an object to be magnified – approx.33%  This is due to the fact that the index of refraction of water is greater than air. This happens behind flat surfaces, such as your mask, a compact camera underwater housing, or a macro port. It does not happen when using a dome port.

Turbidity:
is the cloudiness or haziness of a fluid caused by individual particles (suspended solids) that are generally invisible to the naked eye, similar to smoke in air.

In highly turbid water, objects at a distance appear further away than they appear this is called visual reversal. Turbidity is the most important factor affecting VISUAL REVERSAL

Reflection is the change in direction of a wave front at an interface between two different media so that the wave front returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves The law of reflection says that for specular reflection the angle at which the wave is incident on the surface equals the angle at which it is reflected

Water & Sound

Speed: Sound travels best in dense matter i.e. travels better in water than air. Sound travels 4 times faster in water than in air.
Therefore divers can hear better and at more distance than on air.
It is hard to determine where sound comes from underwater, due to the high speed that sound travels it reaches the eardrums at different times and we cannot work out the direction of sound


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