Backpacks are convenient. They can hold your books, your lunch, and a change of clothes, leaving your hands free to do other things. Someday, if you don’t mind carrying a heavy load, your backpack might also power your MP3 player, keep your cell phone running, and maybe even light your way home.

Scientists from the University of Pennsylvania in Philadelphia and the Marine Biological Laboratory in Woods Hole, Mass., have invented a backpack that makes electricity from energy produced while its wearer walks.

The backpack’s electricity-creating powers depend on springs used to hang a cloth pack from its metal frame. The frame sits against the wearer’s back, and the whole pack moves up and down as the person walks. A mechanism with gears(传动装置) collects energy from this motion and transfers it to an electrical generator.

Surprisingly, the researchers found, people walk differently when they wear the springy packs. As a result, wearers use less energy than when carrying regular backpacks. Also, the way the new packs ride on wearers’ backs makes them more comfortable than standard packs.

The backpack could be especially useful for soldiers, scientists, mountaineers, and emergency workers who typically carry heavy backpacks. These people often rely on global positioning system(GPS) receivers, night-vision goggles(夜视镜), and other battery-powered devices to get around and do their work. Because the pack can make its own electricity, users don’t need to give up space in their packs to lots of extra batteries.

For the rest of us, power-generating backpacks could make it possible to walk, play video games, watch TV, and listen to music, all at the same time. Electricity-generating packs aren’t on the market yet, but if you do get one eventually, just make sure to look both ways before crossing the street!

Some of Australian cyclists have used "GPS art" to turn a 202 km (125- mile) ride into the outline（轮廓）of a goat, which interests many people greatly.

The four men marked their route on an app before using it track their journey around Perth. When uploaded to the computer, it was shown as a picture. Cyclist Ben Jones said the group settled on a goat because it was an easy animal to draw. He said the ride lasted more than six hours, with the four men stopping only for food, and flat tyres . "Except for riding 202km,' it's relatively simple," Mr. Jones told the BBC. "You mainly mark your route on the app and it plans directions out."

GPS art has also been widely used by runners and other cyclists when they travel out. Mr. Jones said his group wanted to shake up their normal weekend ride. "We all ride l0,000km to 15,000km a year," he said. "Mostly we just ride together as mates and have a good time － that's what this was about."

The group received much attention after posting their map to social media this week. Others described Mr. Jones as a goat guy in an interview on Australian television. For their next piece of GPS art, the group plans to draw a local animal such as the koala. "Certainly, there'll be something coming, for we are making our decisions to put more and more plans into practice. I'm sure of that," Mr. Jones said.

When she was 14 years old, Amy’s life was turned upside down by a family trouble.

Amy lived in a small village in India. Her mother fell ill and her father had to spend his time caring for her. As a result, she had to do most of the housework — including washing clothes. What’s worse, her family couldn’t afford an electric washing machine. Instead, she had to do the washing all by hand in the local river, and then carefully carry everything back to her home — a task that took several hours.

Interested in engineering, Amy wanted to make a washing machine which could be used without electricity. She started studying electric washers to learn how they worked. Amy then designed a machine with bicycle pedals (踏板) and chain. To get those, she went to a local shop. Workers there not only gave her the parts, they also helped her make the machine!

Here’s how the machine works: Amy used a cylinder (圆筒) to hold the clothes and put it in a cube (立方体). Next, she connected the bicycle pedals and the chain to the cylinder. As Amy pushed the pedals with her legs, the cylinder cleaned the clothes just like a regular washing machine.

Amy’s invention worked! She had created her own human-powered washing machine — and now a task that used to take several hours took only 30 minutes. Amy’s washing machine was chosen as India’s best invention! And the story of this young woman’s creative invention spread around the world.

“Amy’s invention saves time and money for the world’s poor,” said Jeanine Thomas of the Borden Project, “she made a difference.”