Yet another weird SF fan

I'm a mathematician, a libertarian, and a science-fiction fan. Common sense? What's that?

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Yet another weird SF fan

Monday, June 09, 2014

Help! Help! I Was Run Over by a Cupcake!

As is well known, physics can give counter-intuitive results. As is not so well known, that can happen even in the mundane parts of physics.

For example, let us calculate the energy of a two-ton automobile traveling at 55 mile/hr. This is 24.5 m/s. If two tons is 1800 kg, the standard formula \(\frac{mv^2}{2}\) gives 540,225 J. So far so believable. The counter-intuitive part comes in when we try translating that into Calories. At 4184 Cal/J, 540,225 J becomes 130 Calories, about as much as a large cookie or small cupcake.

No wonder overeating is so dangerous…


Anonymous Cambias said...

What it proves is how immensely inefficient humans (and other animals) are at converting chemical energy to mechanical energy. With the sugar in a can of Coke I should be able to launch the empty can into orbit, but I can barely get it across the room to the trash bin.

. . . which is why any plan to improve "energy efficiency" that involves human-powered transport like bicycles or rickshaws is hilariously stupid.

8:44 AM  
Anonymous Anonymous said...

It's all about the entropy.

There are so many ways to spread a cupcake's worth of energy over the 1e25 molecules in your body that it's amazing they ever get spread in a useful way.

As for spreading a cupcake's worth of energy over the 1e26 molecules in an automobile such that the molecules all have to be going the same way ... that's so improbably it's simply absurd to even consider.

12:19 PM  

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