When President Barack Obama visited Tanzania in early July, he interrupted his tour of a power plant to play with a soccer ball—but not just any old ball. This one generates electricity. The more you kick it around, the longer the charge lasts: 30 minutes of dribbling is enough to give you hours of power for a cellphone or an LED reading light. Four young women studying at Harvard invented the device. They had no engineering experience, but they had a big interest in helping developing countries. They fixed on the idea that 25 percent of the world’s children don’t have good access to electricity but most of them play soccer. If they could convert all that kinetic energy on the playing field into electrical energy, it would be a real breakthrough. With the help of their engineering professors, they developed this ball with a specially adapted generator inside, which they call Soccket, of course. Obama told reporters on his tour that the administration is planning to distribute the balls all over Africa as part of its effort to double access to electricity on the continent.