Auger and Cleave

After the girl had moved the great block with Pry and Ramp and Hoist, she thought she understood simple machines. Then two more rolled up — a screw and a wedge — and they looked nothing like the gentle ramp she'd just used. "Bet you think we're something totally different," said Auger, the spiralling screw. "Bet you can't see the ramp in us," said Cleave, the sharp splitting wedge. The girl squinted. A screw and a wedge, ramps? They didn't look remotely alike. But the two of them were grinning the grin of a very good secret about to be told. "Watch closely," said Auger. "We're both the same old friend — the inclined plane — just in a costume. Every simple machine is really one of a small family, and the ramp is ours."

Auger went first, spinning slowly — because the screw is the sneakiest disguise of all: a ramp wrapped around a pole. "Take a long paper ramp — a nice gentle triangle slope — and now wind it around a pencil, round and round." And Auger showed her: the slope, wrapped into a spiral, became the threads of a screw. "That's all I am. A ramp, wound up. My spiral threads are just an inclined plane going round and round instead of straight up — a helix. So when you turn me, you're really walking something up a ramp — but the ramp is coiled, so instead of a long slope stretching away, it's a long slope packed into a short spiral. You turn the long, easy, round-and-round way — many turns — and I move deep into the wood the short, forceful way. Round and round becomes step and step. It feels like magic, a screw gripping into wood, but it's just Ramp wearing a spiral coat — the same less-force-more-distance bargain, wound up small. The closer my threads, the gentler the ramp, the more turns to go in — and the more force I bite with."

Then Cleave drove forward, splitting a block clean in two — because the wedge is the other disguise: two ramps, back to back, that come to you. "And me? Take two ramps and put them back to back, sharp edges meeting — that's my shape. A wedge — a double inclined plane." Cleave pressed its sharp edge into a block. "But here's my twist on the trick. Pry and Ramp stay still while the load moves along them. I do it backwards — the load stays still, and I move into it. When you push me forward — a long, forceful shove straight ahead — my two ramp-faces turn that forward push sideways, shoving the wood apart to either side. The longer and thinner I am — a fine sharp blade — the more easily I split, but the farther I travel in. Same bargain again: I trade the distance I travel forward for the force I spread sideways." Cleave split the block clean. "An axe, a knife, a chisel, even your front teeth — all of us are just two ramps, back to back, moving into the thing instead of waiting for it."