Growing up in Minnesota, I spent my summers on the lake. Some of my favorite memories are of being pulled on an inner tube behind a boat — the smell of gas from the boat’s engine, the smooth-as-glass water and the initial thrust on the tow rope as the boat lurched my tube forward. To me, that’s summer. What I learned from those picturesque summers (other than which uncle you didn’t want driving the boat), was the power a taut rope has. Or, in other words, the potential energy that comes with a little tension. THE POSITIVE SIDE OF TENSION…