[bregma]

Thank goodness SI units are power-of-ten based so converting between watt hours and joules is just a matter of moving the decimal place. Oh, and throwing in an ancient Sumerian constant approximating the number of Earth rotations as it revolves around the sun once.

[numpad0]

No, Watt-second-hour = 3.6 kJ, so J to Wh is moving the decimal place couple steps AND dividing by 3.6. The actual units used in circuit designs is mAh, so the decimal has to be moved for another time then divided by 3.7[V] again. That's too much for a smooth-brained man like I am.

[lotsofpulp]

Do seconds have anything to do with the Earth rotating around the sun? I thought a second just has to do with the Earth’s rotation on its axis.

Also, I wonder how usable a unit of time that was not based on a day would be, since so much of our life revolves around that cycle.

[tnlnbn]

Yes, seconds are related to the Earth rotating around the sun. Simplifying slightly, the normal definition of a day relates to how long for Earth to rotate on its axis until the same spot on the Earth points at the sun again.

Compare Mean solar day vs Stellar day vs Sideral day - the difference is less than 5 minutes or so.

[lotsofpulp]

Thanks, I see now from:

https://en.wikipedia.org/wiki/Solar_time

I was thinking along the lines of the ancient Sumerians arbitrarily deciding to divide 1 day into 24 hours, and 24 hours into 60 minutes, and 60 minutes into 60 seconds, and how that doesn't have anything to do with how humans came up with the concept of 1 year (the Earth rotating around the sun).