Pressure, Light, and

Sound

Pressure•Atmospheric pressure is the pressure at any given point in the Earth's atmosphere •The standard atmospheric pressure is101.325 kPa.

•Under water, pressure is increased by 1 atmosphere (1 kg/sq cm) every 10 m of depth

• A block of wood at 1000 m deep is compressed to ½ its volume

• Currently, the deepest free dive (as of 2002) was by a Frenchman who dove 175 m– There have been deeper dives (ex.

2007 record of 209.6 m, but it was with the help of a weighted sled)

Light• We see by reflected light; a shirt

appears green because it reflects green and absorbs all other colors.

• There is a color spectrum:–R O Y G B I V–What do you think the colors are?

• Underwater, the deeper you go, the less color you can see.

• The colors will ‘disappear’ as there is less light from the sun.

Water acts as a selective filter. If one were to suspend a white light above a tank of water that was 1000' deep the colors from the white light would be filtered out selectively one-by-one as one descends. It is gradual. For example, most of the red is gone from the light after 10 feet. Some of the orange is gone. Less of the yellow is lost, etc. At 25' most of the orange is gone. At 35' most of the yellow is gone. This continues through the spectrum until all that is left is violet light and that fades out after hundreds of feet. So, at the bottom of this 1000' tank of water there would be little or no light!

Sound• The speed of sound in AIR = 333

m/s• The speed of sound in FRESH

WATER = 100 m/s• The speed of sound in SALT

WATER = 1500 m/s– If salt water is 35 ‰

Echolocation• One of the reasons that echolocation

works so well underwater is because of how fast the sound travels.