Watching his four-year-old son tumble off a two-wheeler every time he slowed down inspired designer Scott Shim to invent a better training tool. At rest, the Shift bike's two back wheels tilt in at the top to form a stable, balance-assisting "A." When the rider leans forward-a natural tendency when pedaling faster-the weight shift activates a tension band that unites the bottom of the rear wheels into, effectively, a single wheel. As the rider slows, the wheels split again. The bike will be available this summer for about $100, minus what you'll save in Band-Aids.
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Science is reinventing play, from extreme sports to gamification to ridiculous roller coasters to the playgrounds of tomorrow, and this issue is chock full of fun. Also, on a less fun note: Did global warming destroy my hometown?