Help Session on Standard MNRG.2.b

This standard states:
I am able to state and apply the First Law of Thermodynamics.

We started out with a Statement of the First Law of Thermodynamics. I followed it up with an alternative version, shown in blue:

first law whiteboard

The 1st Law of Thermodynamics, stated 2 different ways.

Then I showed a way of representing the 1st Law of Thermodynamics symbolically.  Whatever energy goes into any device, system or process is the maximum you can get out after the device or process has transformed the energy.


A symbolic way of stating the 1st Law of Thermodynamics

Then I showed an example of what this means, using a scheme many non-scientists over the years have tried to accomplish–using the output from a generator to power the motor that drives the generator:

perpetual motion machine image

This perpetual motion machine couldn’t power anything.

You can never accomplish anything with a scheme like this, because the very maximum amount of energy the generator could produce is the amount needed to power itself.  (Actually, there is a 2nd Law of Thermodynamics that says you can’t even power the motor with this generator, but that’s another topic for another time.)

Next, we looked at several examples of energy sources we use here on earth to heat ourselves and do work.  It turns out that all the energy (even the “free” stuff we get from renewable methods like solar, wind and biomass) is not created, but originally came from the sun, our big power source for this planet.

energy source image

All the energy sources we use in Earth come from the sun either directly or indirectly.





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