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Courk · Daedalian Member

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

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

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.
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Has anyone really been far even as decided to use even go want to do look more like?

Quailman · His Postmajesty

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.
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Has anyone really been far even as decided to use even go want to do look more like?

Quailman · His Postmajesty

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

Jack_Ian · Big Endian

Who needs pulleys?
Just drive at a 60° angle to the towed vehicle with an arbitrarily long rope. Revenge most foul!

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

Courk · Daedalian Member

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

Okey dokey. Extreme Delectation

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

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

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).

Samadhi · +1

So when the pulling car gets to 44 mph, what happens?
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And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

Courk · Daedalian Member

Adventure.