It’s a screwy world! In this issue, learn how a screw, which is simply an inclined plane wrapped around a cylinder, is just one of the endless varieties of simple machines. For kids, this is an issue that catapults them into action: They’ll want to see for themselves how the wedges, wheels, pulleys and levers described here really operate. Kicking things off, kids encounter the first simple machine: the wedge, which turned up as chisels, axes and arrowheads some 2.6 million years ago. Then it’s on to levers, which are found in everything from scissors to baseball bats, and the wheel, without which we would not have cars and more. Includes teacher's guide and power vocabulary guide.