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If you take a dive light with you on your dive, and shine it on objects at depth, you will be amazed at the colors you will see. Most underwater photographs are made with artificial light (an electronic flash or strobe) to bring out the magnificent, true colors of the underwater world (figures 4-3 and 4-4). Hearing Noises sound different underwater than they do in air. In air, you can tell where a sound is coming from because the sound waves hit one ear slightly before the other. Although the time difference is very short, it is enough for your mind to tell and be able to locate the source of the sound. Because of the greater density of water compared to air, sound waves travel about four times faster in water than they do in air. The sound waves move so quickly that it is difficult to determine the source of a sound. You can hear the sound getting louder or softer, but you cannot tell its direction. When you hear a noise, you must look all around you to see where the noise is coming from (figure 4-5). Boat motors, propellers, and jet skis have distinctive sounds underwater. If you want to surface, but hear a boat or jet ski, stay under as long as safely possible or until you hear the boat or jet ski leaving the area. Remember to always fly a diver down flag and stay within its perimeter to avoid surfacing in the same area as a boat or jet ski. Heat Loss When the air is 27°C (80°F), you think it is warm and comfortable. When you jump into 27°C (80°F) water, the water also feels comfortable at first, but you will notice you start to feel chilled if you remain motionless for a short time. Because water is much denser than air, water can absorb a great deal of heat without changing its temperature. Also, heat can be conducted out of your body by direct contact with water at a rate nearly 25 times faster than by air. NAUI Scuba Diver 96 Diving Science FIGURE 4-3. THE COLORS SEEN WITH NATURAL LIGHT ARE MUTED. FIGURE 4-5. SOUND TRAVELS FASTER IN WATER THAN IN AIR. FIGURE 4-4. ARTIFICIAL LIGHT ALLOWS YOU TO SEE THE TRUE COLOR OF OBJECTS UNDER WATER.


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