Water, wind and kinetic energy
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. This simple waterwheel will not operate in every situation. The
wheel wouldn’t turn in a swimming pool or pond, just as we don’t think about being knocked down by the water, when standing or wading in a swimming pool or a pond. The diﬀerence is that the water isn’t moving in a swimming pool or pond. Only moving water can push against the waterwheel, or push against us. To make a waterwheel move involves work. Only moving water has the capacity for doing work. Water standing still, as in a pool, does not. This means that moving water must possess some kind of energy that allows us to do this work.