Albert sat on a small hill under a tree by a rippling stream thinking about the world around him. He was watching the water ripple over the rocks bouncing around moving as gravity demanded. “What is gravity,” he wanders. “How does it affect the water?”

Sir Isaac Newton was one of the many men of science Albert admired. If the stories were true, Newton was sitting under an apple tree when he first discovered gravity. Later, he developed his three laws of motion, which Albert knew well.

The first law said, an object at rest, such as the apple hanging on the limb, will stay at rest until acted upon by an outside force, such as this mysterious force we call gravity. At the same time a moving object like the falling apple will stay in motion also until acted upon by an outside force, such as hitting Newton’s head. “So,” Albert thought, “at some point gravity exerted a force on the water to get it to start moving. So if there were no outside force then the stream would have never started moving and would have sat still. And when the stream hits the beaver’s damn at the bottom of the hill, it stops.”

Now the second law said, the acceleration of the apple produced by the total force applied, gravity, is directly related to the magnitude of the force in the same direction. So since gravity pulls down, that force was enough at that time to pull the apple from the limb and it accelerated downward. “But why didn’t the apple smash open when it hit Newton’s head?” he wondered. The apple did not have enough mass. He then remembered that acceleration is inversely related to the mass or weight of the object. So the apple did not have enough mass to split open when it struck something. Albert was getting excited by this line of thinking. “Ok, I think I am getting somewhere but is there something more in the third law?”

Lastly the third law said that for every action or force there is an equal and opposite reaction or force. “Now this makes sense. In order for the water to be stopped by the beaver’s damn, the damn has to exert an equal amount of force on the water that it is putting on the damn.” Albert sat forward while images of water, apples, and beavers swirled around in his head.

Finally it occurred to him that if the force of the water hitting the damn was more than the damn could withstand it would break. This would happen during a flood. As the mass of the water increased from rain, it would accelerate and then the force striking the damn would be greater than it could push back on so it would break.

Albert was so happy. At school people made these ideas seems so difficult but to him is was pure and simple fun.


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