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Courk
Daedalian Member

 Posted: Mon Apr 20, 2009 1:26 pm    Post subject: 1 On Mythbusters the other day, they were saying how the pulley set-up they were using allowed them to get their test car to 60 mph while the car pulling that car was only going 30 mph. Can someone explain how a pulley can increase speed?
Zag
Tired of his old title

 Posted: Mon Apr 20, 2009 1:53 pm    Post subject: 2 Well, you know how it can decrease speed, right? Just connect it the other way and pull on what you used to think of as the fixed element. They just have to attach a pulley to their tow car, attach one end of a rope to a fixed object, through the pulley, and the other end to the car they are towing. When the tow car moves 10 feet, the towed car has to move 20, because the rope is doubled. The tow car has pulled the other car by 10 feet, plus the rope between them has shortened by 10 feet.
Courk
Daedalian Member

Posted: Mon Apr 20, 2009 2:18 pm    Post subject: 3

 Zag wrote: Well, you know how it can decrease speed, right?

No, actually.
wordcross

 Posted: Mon Apr 20, 2009 3:42 pm    Post subject: 4 (Definitely not to scale) starts out looking like the left diagram, then end up looking like the right one. The car moving down went 10 ft while the car moving up went 20 ft. The length of rope stays the same._________________Has anyone really been far even as decided to use even go want to do look more like?Last edited by wordcross on Mon Apr 20, 2009 7:42 pm; edited 1 time in total
Quailman
His Postmajesty

 Posted: Mon Apr 20, 2009 4:20 pm    Post subject: 5 Hey, that's a great diagram! I had formulated it in my head a little differently. I had a 200 ft. rope tied to a tree right behind the vehicle to be towed. It ran under the vehicle, 100 ft. to the tow vehicle, through a pulley, and was tied off to the bumper of the vihicle to be towed. When they start, the vehicle being towed would travel twice as fast as the one pulling it, but only for two hundred feet...
wordcross

 Posted: Mon Apr 20, 2009 9:37 pm    Post subject: 6 Your way is actually simpler. I realized after the fact that my fixed pulley was unnecessary._________________Has anyone really been far even as decided to use even go want to do look more like?
Quailman
His Postmajesty

 Posted: Mon Apr 20, 2009 10:05 pm    Post subject: 7 That's one of those direction-changers that my physics teacher would throw into every problem just to mess with us.
Zag
Tired of his old title

Posted: Tue Apr 21, 2009 12:19 am    Post subject: 8

 wordcross wrote: Your way is actually simpler. I realized after the fact that my fixed pulley was unnecessary.

~cough, cough..post...cough...2...cough, cough~
Jack_Ian
Big Endian

 Posted: Tue Apr 21, 2009 1:03 am    Post subject: 9 Who needs pulleys? Just drive at a 60° angle to the towed vehicle with an arbitrarily long rope.
wordcross

Posted: Tue Apr 21, 2009 1:07 am    Post subject: 10

Zag wrote:
 wordcross wrote: Your way is actually simpler. I realized after the fact that my fixed pulley was unnecessary.

~cough, cough..post...cough...2...cough, cough~

And much easier to understand
_________________
Has anyone really been far even as decided to use even go want to do look more like?
Courk
Daedalian Member

 Posted: Tue Apr 21, 2009 1:30 pm    Post subject: 11 I still only fully understand wordy's example, though making progress on the other one. (I learn extremely well with pictures)
Zag
Tired of his old title

 Posted: Tue Apr 21, 2009 2:00 pm    Post subject: 12 Okey dokey. The rope is only 40 ft long. When the tow car moves forward 20 ft, it has pulled the rope by that 20 feet, PLUS the amount of rope between the two cars has shortened by 20 feet to provide length from the fixed point to the tow car. The car being towed was pulled forward by 40 feet. If the tow car goes forward another 20 feet, then all 40 feet of the rope will be used up between the tow car and the fixed point, and the car being towed will crash into the tow car. Since the towed car has moved twice the distance in the same time, it must have been moving at twice the speed.
Loki
Daedalian Member

 Posted: Tue Apr 21, 2009 3:13 pm    Post subject: 13 I found an RC car in my driveway that looks just like an RC car I had in storage. I tried to recreate your pulley diagram with these two cars. It worked, so I wondered if I could string together a hundred little pulleys and travel faster than the speed of light. There were little flaming tire tracks on my driveway and the car disappeared.
Courk
Daedalian Member

 Posted: Tue Apr 21, 2009 10:10 pm    Post subject: 14 I want a remote-controlled pulley-powered DeLorean. Thanks Zag, I get it now. I believe wordy's was the set-up that was actually used (safety and all that).
+1

 Posted: Tue Apr 21, 2009 10:34 pm    Post subject: 15 So when the pulling car gets to 44 mph, what happens?_________________And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.
Courk
Daedalian Member

 Posted: Wed Apr 22, 2009 1:01 pm    Post subject: 16 Adventure.
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