earth as engine
Thermodynamics was the scientific key to the Industrial Revolution: it set down the science of energy, heat, temperature and entropy; it defined at last, after a century of industrial stumbling-about-in-the-dark, the rules of how machines could be made to convert abundant (but not immediately useable) energy into useful work.
Funnily enough, while all these industrialists and scientists were struggling to understand the science of machines, they were actually standing on one. In the 1870s Kelvin (then just plain old Sir William Thomson) pointed out something peculiar about the tides of the earth.
Tides are driven by the varying gravitational attraction of the sun and moon as these and the earth swim gracefully like three big round swans through the heavens: the water on the earth's surface, not being nailed down securely to the planet, tends to slew around a bit.
Kelvin noticed, however, that there was something else that affected the exact motion of the oceans: the pressure of the air. As the tide of water sweeps in to the beach, it fights against air pressure weighing it down.
Hence changes in air pressure change the way the oceans shift. And it was known that air pressure varied between day and night--for the simple reason that the sun heats the air during the day and doesn't during the night. The upshot of this, Kelvin realised, was that the day-night cycle of radiated heat from the sun was converted into a day-night cycle of mechanical force (air pressure) which acted, just like a motor going round or a piston going up and down in a car engine, to cyclically force the motion of the oceans.
This is exactly what any engine does: for instance, a steam engine, the classic workhorse of the 19th century and the icon of the industrial revolution, uses heat from a fire to turn water into steam, generating pressure large enough to drive a piston in a cylinder--generating mechanical force. As the steam cools and condenses, air pressure drives the piston back into the cylinder. And then around again: heat, push out, cool, push in... Heat into mechanical work, all in a cyclic process.
Hence the cyclic heat-cool/push-pull of the air pressure on the oceans means the whole earth is a gigantic motor: converting, by means of air pressure, heat from the sun into a cycle of mechanical force on the water.
We live on the surface of a vast engine!
Funnily enough, while all these industrialists and scientists were struggling to understand the science of machines, they were actually standing on one. In the 1870s Kelvin (then just plain old Sir William Thomson) pointed out something peculiar about the tides of the earth.
Tides are driven by the varying gravitational attraction of the sun and moon as these and the earth swim gracefully like three big round swans through the heavens: the water on the earth's surface, not being nailed down securely to the planet, tends to slew around a bit.
Kelvin noticed, however, that there was something else that affected the exact motion of the oceans: the pressure of the air. As the tide of water sweeps in to the beach, it fights against air pressure weighing it down.
Hence changes in air pressure change the way the oceans shift. And it was known that air pressure varied between day and night--for the simple reason that the sun heats the air during the day and doesn't during the night. The upshot of this, Kelvin realised, was that the day-night cycle of radiated heat from the sun was converted into a day-night cycle of mechanical force (air pressure) which acted, just like a motor going round or a piston going up and down in a car engine, to cyclically force the motion of the oceans.
This is exactly what any engine does: for instance, a steam engine, the classic workhorse of the 19th century and the icon of the industrial revolution, uses heat from a fire to turn water into steam, generating pressure large enough to drive a piston in a cylinder--generating mechanical force. As the steam cools and condenses, air pressure drives the piston back into the cylinder. And then around again: heat, push out, cool, push in... Heat into mechanical work, all in a cyclic process.
Hence the cyclic heat-cool/push-pull of the air pressure on the oceans means the whole earth is a gigantic motor: converting, by means of air pressure, heat from the sun into a cycle of mechanical force on the water.
We live on the surface of a vast engine!
posted by mark haw at 11:28 am
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