Hovercrafts, once a thing of sci-fi and fantasy, are now a reality. Thames & Kosmos offers kids the opportunity to build their own working hovercraft that glides across smooth floors or flat water on a cushion of air with the Air Stream Machines kit. Under the right circumstances, air can support heavy objects because even though it is invisible, it still has mass. The kit teaches kids about air mass and air pressure by letting kids experiment with propellers, impellers, blower motors, and fans. Kids can even build a batting machine that suspends a ball on top of the stream of air, a basketball launcher, or a fan-driven car.