Backpack generates power through walking

• Their backpack design converts mechanical energy from the up-and-down movement of the backpack's cargo to electricity during normal walking.
• Fueled by a snack, hikers can put the spring in their steps to good use, the researchers write in Friday's issue of the journal Science.
• The backpack is deliberately designed to shake around a bit.
• The up-and-down movement of the backpack's cargo compartment against the frame of the pack turns a gear connected to a generator.
• The simple magnetic coil generator is similar in principal to those seen in hand-cranked radios, flashlights that work after a rhythmic shaking and other devices.
• Trodding along under a hefty 85 pounds of weight in the backpack can produce up to 7 watts of electricity, Lawrence Rome and colleagues at the University of Pennsylvania report.
• This is more than enough electricity to simultaneously power an MP3 music player, a personal digital assistant, night vision goggles, a handheld Global Positioning Satellite navigation device, and a mobile telephone.
• Human hips rise and fall about 2 inches with each step, and a backpack worn by a person who is walking rises and falls as well, they said.
• "As humans walk, they vault over their extended leg, causing the hip to rise 5 to 7 centimeters on each step.
• "It is this vertical movement of the backpack that ultimately powers electricity generation."
• But nothing is free, so what does this energy cost the hiker?
• "Metabolically speaking, we've found this to be much cheaper than we anticipated.
• The energy you exert could be offset by carrying an extra snack, which is nothing compared to weight of extra batteries," Rome said.
• "Pound for pound, food contains about 100-fold more energy than batteries."