Begin the lesson by showing students how complicated currents can be. Mix one quart of white Ivory dishwashing liquid with five drops of food coloring. Place several small rocks in a shallow baking pan, then tilt the pan up at one end. Pour the liquid in and watch the pattern of currents flowing around the rocks. The more swirls, the more turbulent the water.
Few sights reveal nature's power as clearly as rapids in a fast-flowing river.
Water pounds against rocks, sprays into the sky, and boils into white froth. The thought of rafting through such turbulence is scary-unless you are an experienced river runner. Rapids look chaotic, but they are predictable. Experts can read a stretch of rapids, spotting the hazards and seeing the safest way through. Knowing the amount of water flowing in a river is important because the river's speed increases as more water flows through it.