As divers, we have to deal with the effects of water density. Water is about 800 times denser than air, and the first effect noticed by most people is the increased effort required to move while in the water. But this is just one effect of water density. Objects appear differently, sounds are more pronounced, and you get cold faster. In this lesson, you'll learn about the density of water and how it affects us as divers.

After this lesson, you will be able to:

• State the density of fresh and salt water.
• Explain two effects of water density on light.
• Explain how water density affects sound.
• Compare the rates of heat loss in water and air.
• List two ways to reduce drag underwater.