科学美国人60秒：物理学帮你解决拉杆箱翻倒问题
燕山大学 刘立军 宋葳 编写
◆TRANSCRIPT
This is Scientific American - 60-Second Science. I'm Christopher Intagliata.
If you've ever pulled a rolling suitcase through the airport, chances are you've also been annoyed by this common occurrence: the suitcase starts rocking back and forth on each wheel and finally tips over.
"It's a very classic phenomenon in physics." Sylvain Courrech du Pont, a physicist at the University of Paris Diderot. "So if you perturb the system it goes very easily unstable. This is shared by many, many phenomena in nature."
Courrech du Pont and his students wanted to get to the bottom of why luggage tips. So they built what looks like the skeleton of a wheeled suitcase, and then filmed it rolling on a treadmill. Then they modeled what they saw mathematically.
And here's what they found. Under normal rolling conditions, the forward motion of the suitcase is perpendicular to the wheels' axis of rotation. All good. But when you hit a bump or jerk the handle, one wheel lifts up. All of a sudden the pulling motion is no longer perpendicular to the still-rolling wheel's rotation, and the wheel corrects that by drifting towards the center. But by that time the other wheel's coming down, same thing happens, and now the suitcase is really rocking.
"And the first reaction you will have maybe is to slow down. But actually if you slow down you'll experience very big rocking oscillations." The way back to a smooth ride, he says, is to keep up your speed, or move even faster, once rocking begins. The study is in the Proceedings of the Royal Society A.
There are other solutions to suitcase instability - like doing a better packing job. "If you put heavy stuff close to the axis of symmetry, or close to the wheel axis, then it's stable, too."
And Courrech du Pont has one more piece of advice to avoid rocking in the first place: "If you go slow enough it will always be stable." Keep that in mind, next time you're running to your gate.
Thanks for listening for Scientific American - 60-Second Science. I'm Christopher Intagliata.
Adapted from http://www.kekenet.com/broadcast/201710/526489.shtml
◆VOCABULARY
1. perturb v. (动词 + 名词短语) (formal) to make sb. worried or anxious 使焦虑；使不安。例如：Her sudden appearance did not seem to perturb him in the least. 她的突然出现似乎一点也没有令他不安。
2. treadmill n. (可数名词) (especially in the past) a large wheel turned by the weight of people or animals walking on steps around its inside edge, and used to operate machinery （尤指旧时由人或牲畜踩动踏板使之转动的）踏车
3. oscillation n. (不可数名词, 单数) a regular movement between one position and another or between one amount and another 摆动；摇摆；振动。例如：
○the oscillation of the compass needle罗盘指针的摆动
○the economy's continual oscillation between growth and recession经济增长与衰退之间的持续波动
4．tip over: to fall or turn over; to make sth. do this （使）跌倒，倾覆。例如：
○The mug tipped over, spilling hot coffee everywhere. 杯子倒了，热咖啡溅得到处都。
○We'll have to tip the sofa up to get it through the door. 我们必须把沙发翻转过来才能搬过房门。
◆QUESTIONS
Read the passage. Then listen to the news and fill in the blanks with the words you hear.
This is Scientific American - 60-Second Science. I'm Christopher Intagliata.
If you've ever pulled a rolling suitcase through the airport, chances are you've also been annoyed by this common occurrence: the suitcase starts (1) ________________________ on each wheel and finally (2) __________________.
"It's a very classic phenomenon in physics." Sylvain Courrech du Pont, a physicist at the University of Paris Diderot. "So if you perturb the system it goes very easily unstable. This is shared by many, many phenomena in nature."
Courrech du Pont and his students wanted to get to the bottom of (3) ___________________. So they built what looks like the skeleton of a wheeled suitcase, and then filmed it rolling on a treadmill. Then they modeled what they saw (4) ________________________________.
And here's what they found. Under normal rolling conditions, the forward motion of the suitcase is (5) _________________________________ to the wheels' axis of rotation. All good. But when you hit a (6) ___________________________ or jerk the handle, one wheel lifts up. All of a sudden the pulling motion is no longer perpendicular to the still-rolling wheel's rotation, and the wheel corrects that by drifting towards the center. But by that time the other wheel's coming down, same thing happens, and now the suitcase is really (7) __________________________.
"And the first reaction you will have maybe is to (8) ________________. But actually if you slow down you'll experience very big rocking oscillations." The way back to a smooth ride, he says, is to (9) ___________________________, or (10) ________________________________, once rocking begins. The study is in the Proceedings of the Royal Society A.
There are other (11) ___________________________ to suitcase instability - like doing (12) _________________________________. "If you put (13) __________________________ close to the axis of symmetry, or close to the wheel axis, then it's stable, too."
And Courrech du Pont has one more piece of advice to (14) _____________________________ in the first place: "If you (15) _____________________________ enough it will always be stable." Keep that in mind, next time you're running to your gate.
Thanks for listening for Scientific American - 60-Second Science. I'm Christopher Intagliata.
◆KEY
This is Scientific American - 60-Second Science. I'm Christopher Intagliata.
If you've ever pulled a rolling suitcase through the airport, chances are you've also been annoyed by this common occurrence: the suitcase starts (1) rocking back and forth on each wheel and finally (2) tips over.
"It's a very classic phenomenon in physics." Sylvain Courrech du Pont, a physicist at the University of Paris Diderot. "So if you perturb the system it goes very easily unstable. This is shared by many, many phenomena in nature."
Courrech du Pont and his students wanted to get to the bottom of (3) why luggage tips. So they built what looks like the skeleton of a wheeled suitcase, and then filmed it rolling on a treadmill. Then they modeled what they saw (4) mathematically.
And here's what they found. Under normal rolling conditions, the forward motion of the suitcase is (5) perpendicular to the wheels' axis of rotation. All good. But when you hit a (6) bump or jerk the handle, one wheel lifts up. All of a sudden the pulling motion is no longer perpendicular to the still-rolling wheel's rotation, and the wheel corrects that by drifting towards the center. But by that time the other wheel's coming down, same thing happens, and now the suitcase is really (7) rocking.
"And the first reaction you will have maybe is to (8) slow down. But actually if you slow down you'll experience very big rocking oscillations." The way back to a smooth ride, he says, is to (9) keep up your speed, or (10) move even faster, once rocking begins. The study is in the Proceedings of the Royal Society A.
There are other (11) solutions to suitcase instability - like doing (12) a better packing job. "If you put (13) heavy stuff close to the axis of symmetry, or close to the wheel axis, then it's stable, too."
And Courrech du Pont has one more piece of advice to (14) avoid rocking in the first place: "If you (15) go slow enough it will always be stable." Keep that in mind, next time you're running to your gate.
Thanks for listening for Scientific American - 60-Second Science. I'm Christopher Intagliata.