NEW YORK — The Dec/Jan issue of Popular Science is on newsstands and the iPad on December 19th

Can We Outlaw Fossil Fuels? Hawaii is trying, and they want to get it done by 2045. Is it smart—or crazy stupid—to rely solely on wind, solar and hydro? The challenges are many, but Elemental Excelerator, a nonprofit that finds, funds and nurtures the inchoate technologies that can extinguish our country’s fossil fuel habit, is hoping to make it happen (page 34).

What Is Horsepower? In 1781, James Watt needed to convince skeptics to ditch draft horses and buy his new steam-engine. To prove his machine’s superiority, he measured a horse walking in circles to turn a grindstone in a mill. He multiplied the distance it walked by its roughly 180 pounds of pulling force and came up with a new measure: horsepower (page 8).

Why Can’t We Decide What to Do About Nuclear Energy? We may be facing what looks like the beginning of the end of America’s nuclear-energy ambitions. Many plants could close thanks to competition from cheap natural gas, the rising affordability of wind and solar generation, and fear of radiation-spewing accidents. But closing a nuclear power plant isn’t as simple as just locking the doors and walking away (page 56).

Pedal Pushers Huffing and puffing a bike up a hill is a thing of the past in the lithium-ion era. E-bikes (standard two-wheelers with motors in their frames) can boost your cruising speed to 28 miles per hour; only if the battery dies, do you rely on your old-fashioned legs. Here are PopSci’s favorite souped-up whips that can tackle any terrain (page 24).

The Fault in Our Star The sun can cripple communications (think: GPS routes, small-craft plane navigation, SiriusXM service) and knock out the grid anywhere. When it does, the internet will find out about it from the Space Weather Woman, Tamitha Skov. She hosts a web series that explains space’s weather, and its effects here on Earth. (page 49).

Gone in Two Seconds The push that kick-starts a bobsled run is arguably the most powerful moment in any Olympic sport. Popular Science dove into the ideal form, equipment, and conditions that contribute to the pivotal couple of seconds on the course (page 54).

Roar How will Formula One —the world’s fastest and most popular motorsport—reckon with a (quietly) surging electric tide? Will the most advanced racing series in the world still drive the innovations that power our road cars, or will it instead become pure sport, with entertainment as its singular goal? Or could an all-electric championship overtake F1 as the fastest R&D lab on Earth (page 42)?