A Physics Lesson

I had to get straight As in second grade to earn my three-speed bike, but that didn’t mean that I understood the laws of physics. However, after getting the bike I began to learn physics, even if only implicitly. Unfortunately, most of those lessons involved some kind of bodily injury.

My new bike was a mechanical marvel. It had many abilities that my previous bike did not have, and I was intent to understand each one of them. The gearing system allowed me to go much faster, and I easily outraced every kid in the neighborhood. It even had a speedometer, and I delighted in seeing how fast I could go.

I was determined to get my speed up to twenty miles per hour, which seemed impossible on the flat terrain of our neighborhood. But I finally found a hill that allowed me to achieve this daredevil speed.

The bike came equipped with both front and rear brakes that were applied with levers on the handle bars. The levers moved rubber pads that pressed against the tire rims and slowed the bike. I could slow the bike with much more control that my old bike. I could stop on a dime or gradually slow.

I felt in control of the universe.

One afternoon I was sitting in Kevin’s front yard, trying to figure out something new to do with my bike. His driveway was directly across from the hill that had helped me achieve my highest speed yet.

“I know what I can do,” I said with sudden inspiration.

Kevin sat up excitedly. He lived vicariously through my stunts. “What?”

“If I come down the hill and into your driveway, I bet I can get up to twenty-five. How cool would that be?”

“That would be great. I bet you can do it. My driveway is pretty long.”

That was all the encouragement I needed. I hopped on my bike and pedaled to the top of the hill. As I turned around, I was convinced that this would be the best thing I’d ever done. I looked at Kevin one hundred yards away at the end of his driveway and he waved.

 

I pushed off and was quickly into third gear, which increased the torque applied and my speed. I glanced at the speedometer as I entered Kevin’s driveway. I giggled when I saw that I was going twenty-seven. Maybe I can hit thirty, I thought, pumping my legs even harder.

I heard Kevin yelling at me, but I couldn’t discern his words as I rushed past him. I thought he was cheering me on. And then I realized what he was shouting. “Stop. Stop. Stop.”

At that point, it became clear that I hadn’t thought this through very well. The end of the driveway was thirty yard away and rushing towards me. At the end of the driveway stood a wall of boxwoods. A million thoughts flashed through my young mind, and none of them were good. I was going to die. Or worse, destroy my new bike.

I was fifteen yards from the wall of shrubs. I desperately looked for somewhere to turn. But the boxwoods stretched forever in each direction. This was too much for me to process. I wished for some kind of miracle, but a miracle didn’t seem to be imminent.

And then Kevin’s words resounded in my ears. Of course, I thought. I should stop. I had two brakes. I closed my eyes five yard from the shrubs and squeezed the brake levers with every ounce of strength my shaking body could muster.

That is when I personally experienced Newton’s First Law of Motion: A body in motion will continue to move until something stops it.

In my particular situation, the brakes stopped the bicycle from moving. But the brakes did not stop my forward momentum. As my legs lifted off the pedals and began to rise behind me, I realized that I had another decision to make rather quickly. Should I hold onto my bike or let go?

As it turned out, it really wasn’t a decision for me to make. The force of my body being catapulted over the handle bars was more than my hands could sustain. My hands were ripped from the handle bars as my body became airborne.

What a way to die, I thought. Trees, shrubs, and the blue sky whizzed through my field of vision. And then my motion stopped as my feet hit the ground. I shook my head and looked around. I was on the other side of the boxwoods. I was alive! And on the other side of the shrubs, Kevin was clapping. “That was cool. Do it again,” he shouted.

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