ABSTRACT
Think about wading in a fast-moving stream, or standing in surf feeling the waves break against you. The ‘push’ of the water might be so strong that a person could be knocked down by the rushing water. Think about a simple wheel with paddles on it. When it is partially immersed into a flowing stream, water will push against the paddles, just as it pushes against us. The ‘push’ of the water against the paddles will cause the wheel to turn. By connecting the shaft of the wheel to some piece of machinery, we can do useful work.
