Musings

A food Calorie (capital "C") is actually a kilocalorie, or a thousand calories.

A calorie is by definition enough energy to heat one gram of water one degree C.

So a food Calorie is enough energy to heat one thousand grams of water one degree C.

A gram of water is by definition one cubic centimeter, which is one mL. A liter of water is thus one thousand grams of water.

A piece of Pilot Bread:


is one hundred food Calories, or 100,000 calories, enough to heat a liter of water a hundred degrees C.

Does this make sense to anyone? Zero degrees C is freezing; a hundred degrees C is boiling. A single piece of Pilot Bread can, theoretically, heat a liter of water from freezing to boiling.

?!?

Our bodies must be astonishing at accessing chemical energy, because I cannot even imagine boiling a liter of freezing water on the wood stove by burning a single piece of Pilot Bread!

I thought of something else...

I am roughly 61 kg, which is 61,000 g. Assuming that I am all water (since I am about 60% water), and these numbers are all rough, that means that I am 61 liters of water.

My body temperature is 37 degrees C, or 63 degrees below boiling.

To heat 61 liters of water 63 degrees C, it takes 3,843,000 calories, or 3843 food Calories. That means, in theory, every time I eat 3843 food Calories, I can boil myself!

And then I thought of something else...

I am roughly 165 cm tall. My waist is approximately 70 cm around. Approximating me as a cylinder whose circumference is the circumference of my waist, my surface area is about 12,000 cm^2. However, because I am not a cylinder, and have two legs and two arms and fingers and a neck and such, let's multiply by, say, 1.2 to get a better number. So my surface area is 14,400 cm^2, or 1.44 m^2.

Convective heat transfer between a surface and air is given by:

q = h A (deltaT),

where q is the energy transfer, in energy per area per degree of temperature.
h is an empirically derived coefficient that ranges from 5-20; I'll pick 10 as an arbitrary, mid-range guess.
A is the surface area.
deltaT is the difference in temperature between the surface and the air. I'm pretty happy with an air temperature of 18 degrees C, so we'll use 37-18=19 for my deltaT.

So my q is 10 * 1.44 * 19 = 273 Watts, which is Joules per second, which is 65.2 calories, or 0.0651 food Calories, per second.

That translates to 5625 food Calories per day (24 hours) to keep me warm, based on my really rough numbers.

I don't eat nearly that much, but I got close to the order of magnitude, which is cool!