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Why I’m glad I paid attention in chemistry

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Yesterday, I replaced the thermostats on my water heater, and since I had to turn the power off for that, I decided it would also make sense to flush it since it’s about 6 years old. Anyway, drained it completely, ran cold water through it for about 10 minutes, then filled it back full of cold water, and turned on the power.

I was kind of surprised that it took over an hour to completely heat the water. Then today, I started thinking about it and thought “wait a second! I minored in chem. I should be able to calculate this”. So, let’s see what we know, and then do some basic math!

Knowns:

  • Water heater size is 50 gallons
  • Element size is 4500 watts
  • Incoming water temp (ground water) is 61F (right now)
  • Water heater thermostat is set to 115F

Since we’re dealing with Imperial units here, we’ll stick with them (as painful as that may be).

  • 1 gallon weighs 8.345 pounds (lbs)
  • 1 watt/hour is equal to 3.412 BTUs

Quick definition of BTU: “The quantity of heat required to raise the temperature of one pound of water one degree at a constant pressure of one atmosphere”.

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The Portal problem

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After playing Portal 2 co-operative through, a friend and I were chatting and realized a bit of an issue with the physics in Portal, and neither of us were sure if this is something Valve even thought of when producing the games.

The graphic to the left ((images for this post were generated with Omnigraffle using a stencil I produced from vector images obtained from here. All are unofficial)) shows a situation where in Portal 1 and 2 ((Portal is a registered trademark of Valve Software)), you could put a portal on the ceiling, and one on the floor, and basically fall “forever”. But, for those that have done it, you’ll remember that there was a terminal velocity that was reached where you couldn’t fall any faster. Terminal velocity being the speed at which the air resistance of the falling object is great enough to counteract the gravity that’s pulling the object down. And that rate changes based on the shape of the object (so a person falling with hands at his/her side, legs together, pointed down, will fall faster than someone falling spread out, chest down).

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