What Powers a Trebuchet?

Posted: August 6, 2011 in Random Thoughts
Tags: , , , , ,
Trebuchet
We have a small garden in out back yard and a few of the plants have been eaten to death by slugs. Those slimy little buggers have destroyed two of the delphinium plants and I was thinking about various ways to make the slugs atone for their malefaction. Initially I had considered walking around with a salt shaker but that just seemed too mean not to mention their little slug corpses would be all over the back yard. That’s when I thought it would be fun to make a little slug Trebuchet to fling the little slimers into the neighbor’s yard. I found this idea very humorous and was imagining the little slugs sailing through the air into the neighbor’s yard and far away from my garden. As usual when I start thinking, I considered how the Trebuchet works and I wondered what powers it.
At first glance you would probably think that gravity powers the Trebuchet. Gravity pulls down the heavy counterbalance and the Trebuchet throws things. I suppose that is correct in some respect but it’s not as if the Trebuchet will just randomly fire because of gravity. Gravity is just the force but the potential energy of the counterbalance comes from its position relative to the gravitational field of the Earth. What gives the counterbalance its potential energy? In most cases, this potential energy is added to the system by people lifting the counterbalance into the air. That’s a fun thought. It’s people power that actually flings things through the air.
Once you start thinking about where the energy comes from, you can’t really stop with people because the next question that comes to mind is where did the people get the energy? We all know that people have to eat to get their energy. It appears, then, that the Trebuchet is really hamburger powered. That is a really fun thought. But we can’t stop there either because we need to know from whence the food obtained its energy. In this case you need to follow the food chain which will eventually lead you to plants. So my slug Trebuchet is really plant powered? Not really, because again we need to consider where the plants get their energy. Plants get their energy from the Sun and conveniently save some of the left over energy in chemical batteries (starches and sugars) that we eat to get our energy. So plant energy comes from the sun… That means that my Trebuchet is really solar powered!
By this point, I’m sure you can see what is coming next: Where does the Sun get its energy? This is where it gets interesting. The first thing you’ll probably think of is that the Sun gets its energy from nuclear fusion and that’s more or less correct. So that means the slug-flinger is fusion powered! But fusion requires lots of energy to get started; our fusion bombs require a fission explosion to provide enough energy for fusion to occur. Where did the Sun get the energy it needed to start fusion? During the formation of the Sun, gas and dust started to form lumps because of gravitational attraction between the particles. These lumps combined to form bigger and bigger lumps until eventually a really huge lump was formed. In this huge lump gravitational forces put huge pressure on the particles inside the lump and they heated up. Eventually the particles became so energetic they started to combine nuclei and fusion started.
So gravity* started the fusion that started the Sun which sent energy to the plants on Earth that stored the energy as starches and sugars that people ate so that they could lift the counterbalance on the Trebuchet to give it potential energy which was converted to kinetic energy by the Earth’s gravity which flings the slugs into my neighbor’s yard so they stop eating my plants.
*You could ask what gives gravity its energy or rather why things clump together but we’ll have to wait on the LHC for the answer to that one.
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