The piston is an amazingly simple, ridiculously useful and successful mechanism that, together with a connecting rod and crankshaft, converts linear motion to rotational motion.

This simple system is basically what allows us to take a force produced by, say, steam or an explosion and make a wheel turn. Stick a few of these together and time the rotation of each correctly, carefully controlling the explosions and the exhaust, and you have an internal combustion engine that powers and moves our cars.

There are a lot of amazing things to me about it, but I am still impressed with how effectively it takes something moving back and forth and makes something spin around and vice versa.

The piston

The half-life of caffeine is about 4 hours.

The data vary, but for a medium-sized adult, you can probably expect half of the caffeine from that 3 pm cup of coffee to still be doing half of its thing about 7 pm, 4 hours later. Apparently, smokers deal with caffeine quicker, and caffeine sticks around in children much longer.

You can expect about 10 minutes before it first kicks in, which, I suppose, is why if you’re feeling tired while driving, it’s a decent plan to take a break and drink a coffee, then have a 15-minute nap. See tiredness can kill, take a break. Once it starts to kick in, you might hit peak caffeine any time from 45 minutes to 2 hours later.

Caveat: The chart visualisation is extrapolated from reported data, so the shape is only approximate.

Some references say longer, and some say from 3-9 hours or so. My source, which seemed pretty comprehensive, was:

Bertil B. Fredholm, Karl Bättig, Janet Holmén, Astrid Nehlig and Edwin E. Zvartau, Actions of Caffeine in the Brain with Special Reference to Factors That Contribute to Its Widespread Use, Pharmacological Reviews March 1999, 51 (1) 83-133;

The half-life of caffeine

For a closer look next time you’re at the beach. Pay close attention to whether you find one with a dextral or sinistral aperture.

Gastropods are the largest class of molluscs which includes limpets, snails and sea slugs. For those who weren’t sure.

Info from the 1971 book, Discovering Sea Shells by Barry Charles

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Typical gastropod anatomy