My second grade teacher had a pair of supermagnets. She wowed us with them one day, lifting a metal barstool by just holding onto the tiny silver nub. We were allowed to play with them only when closely supervised. Apparently, a couple years back, a girl had pointed one magnet at the other from across a table, and it had zipped up and hit her in the face.
Ferrofluids are made up of tiny magnetic fragments of iron suspended in oil (often kerosene) with a surfactant to prevent clumping (usually oleic acid). The fluid is relatively easy to make at home yet extremely expensive to buy on-line. How does $165 a liter sound? Pretty bad, right? Read on to learn how to make ferrofluids on the cheap.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.