fig

food_energy.tex

@@ -86,10 +86,34 @@ height &\approx&  1000 m
 \eea
 This estimate is again surprising to students.  Five trips up the bluff to burn off $\$2$ of saturated fat, sugar, and flour!  A nice followup calculation is to imagine a car that can burn a $100kcal$ piece of toast -- from rest, what speed will the toast propel it to? If (again) the engine converts $1/3$ of the energy into motion (kinetic energy), a 1300kg Honda Civic will reach a speed of about $13\frac{m}{s}\approx33mph$!  
 
-The point of these energy conversion calculations is not to give students an eating disorder.  Rather, they are meant to illustrate how powerful and amazing the food we eat is.  A single slice of toast will bring a car up to the speed limit on a residential road!  Food and our bodies are amazing, and increases in food production have made our comforts, unimaginable 150 years ago, possible and taken for granted.  
+The point of these energy conversion calculations is not to give students an eating disorder.  Rather, the numbers show food's amazing power. A single slice of toast will bring a car up to the residential speed limit!  A day's food, $3000kcal$, will power you up an $8000m$ peak! The body-work food allows us to do is astonishing, and increases in food production have made modern  comforts, unimaginable 150 years ago, possible to the point of being taken for granted.  
 
-increase in yields since 1917 (graph)
+\subsection{Where does food energy come from?}
+One modern feature of the aught's ``homesteading'' culture is the idea that a person can probably move to the country and grow all their own food.  Learning that farming labor is \textit{skilled} labor can be a brutal and disheartening realization. $3000kcals$ each day is about is one million kcals each year.  Where will those Calories come from? Is your backyard enough to homestead in the suburbs?
 
+At some point bewteen 1920 and 1950 US chemical manufacturers realized that in the post-war period, they could repurpose chemical processes developed for chemical warfare and munitions to produce chemicals that would kill insects and increase the Nitrogen levels in the soil. As figure \ref{ag_yields} shows, a dramatic increase in per-acre yields has ocurred across all comodity food crops.  
+
+\begin{figure}[h]
+\centering
+\includegraphics[width=\columnwidth]{bar_chart.png}
+\caption{
+USDA yields
+}
+\label{ag_yields}
+\end{figure}
+
+If you're discussing backyard Calorie production it isn't reasonable to use modern yield estimates for planning.  ``Roundup Ready'' Corn, Soybean, and Sugar Beet seets are not available to the public, and the edge effects from deer and insects are much smaller on a 600acre field than they are in an community garden allotment.  As mentioned in the introduction, in 1917 the USDA published a pamphlet, shown in \ref{1917_yields} about yields a farmer might expect.  Their data came from pre-war, pre-chemical agriculture, and the yields cited were produced with horses, manure, lime, and large families full of children.  If you want to be self sufficient, these yield numbers are probably a good upper bound on what's realistically possible.  
+
+\begin{figure}[h]
+\centering
+\includegraphics[width=\columnwidth]{bar_chart.png}
+\caption{
+USDA yields from pre-chemical US ag
+}
+\label{1917_yields}
+\end{figure}
+
+So, another question using this data.  If you want to feed your family of 4 potatoes, how much land will you need to cultivate?
 1917 data
 
 Grow your own food, possible?