Energy, Work, and 12 Points of Learning
by: Paul Kando
My father loved work. He involved me in it almost as soon as I could walk. He
would explain the task at hand and ask how I would address it. He'd listen to whatever
I had to say, we'd discuss it and agree on how to proceed. Every Sunday morning Apa
would open the glass door of the beautiful, tall grandfather clock we had in our
Budapest apartment (before World War II blew it all away) and wind the clock by
raising the shiny, brass-covered weights back to the top.
Why don't we install an
extra weight? - I ventured one day.
The other weights would pull it up, and on
the way down it would wind the clock.
I am afraid that wouldn't work, Apa replied.
Look, this weight weighs the same, whether it is on top and doing the work of making
the clock run, or at rest on the bottom with the clock stopped. The difference is
that on the bottom the weight can no longer do any work. A perpetual motion machine
is impossible because everything in the universe wants to reach equilibrium - the
weight wants to come to rest, rain wants to stop falling, a warm house wants to
cool until it is as cold as it is outside. That was my first lesson in physics.
In four brief sentences, Apa taught me two laws of thermodynamics -- #1, the law
of conservation of energy and matter; and #2, the law of entropy.
I thought of this on Labor Day. It's back to work. The visitors are gone. The
kids are starting school. The red squirrels are busy preparing for winter and
grasshoppers are queued up at the door, hoping to get inside. Thoughts turn toward
connections, not always intuitively apparent, between work, learning, energy,
and, for me, emails about the coming winter. A typical exchange:
the basement ceiling? The boiler produces heat that rises through the basement
ceiling to the next floor. Insulating the basement ceiling cuts off this heat
migration and preserves it for the basement rather than sharing with the rest of
the house. Why is that a good thing? The short answer:
In accord with the second
law of thermodynamics heat does not rise. It moves from hot to cold in all directions.
Therefore your (hopefully) warmer living room will heat the basement, not the other
way around. It is warm air that rises, not heat, because, when heated, air expands
and becomes lighter by volume.
Where do myths like "heat rises" come from? Now that "home efficiency improvements" are finally in vogue, people who don't understand the basic physics of energy, house and climate, are easily taken advantage of. The consequences can be dire, such as serious moisture damage to the home, if home energy fixes are done piecemeal, rather than dealing with the house as a system. It is perfectly OK to make gradual improvements as we can afford them, but if compromises must be made for affordability reasons, they still must make technical sense. For example, adding ½" of foam insulation under a new siding instead of 4", is worse than adding no insulation at all, because water vapor trapped within the wall cavity will cool below the dew point and condense, guaranteeing the slow destruction of the exterior wall due to rot.
Therefore, if I, (who admittedly benefitted from an education with no electives until college, and compulsory physics, chemistry and biology from the 5th grade on) had my say, all Maine fifth graders and older would understand the following 12 basic points and know how to apply them:
- Energy is the capacity to do work, and heating something is work.
- Energy cannot be created or destroyed, but it can be converted from one form to another.
- Energy's capacity to do work diminishes; energy flows from high work-capacity to low.
- All energy on Earth originates from the Sun. Sunshine is electromagnetic radiation, which, as it impacts matter, is converted to heat, another form of energy.
- Heat, air, and water interact. These interactions produce conditions that sustain life, the climate, the weather, and comfort conditions inside a house.
- When air is heated, it expands, becomes lighter by volume, and therefore rises.
- When water is heated, it evaporates.
- Air absorbs water vapor. The warmer the air, the more vapor it absorbs (relative humidity).
- When air cools, it releases any water vapor it can no longer hold; and when water vapor cools, it condenses into liquid water.
- When things cool, they release the energy they have absorbed by warming: no energy is lost.
- The warmer the ambient temperature of the planet, the more air is warmed, the more water is evaporated, the more vapor is absorbed, and, eventually, the more vapor condenses and the more energy is released. The result: a climate with more severe weather events.
- Heat travels by radiation, conduction, and convection. To prevent heat loss in a house we must air seal (to prevent convection), insulate (to retard conduction and radiation), provide ventilation (to prevent the buildup of moisture and stale air), mitigate thermal bridges and use energy efficient windows and doors (to further control conductive heat losses).
The idea is to observe and understand. Forget testing.