h a l f b a k e r yNot so much a thought experiment as a single neuron misfire.
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Cars drive up a hill and get into a ferry. The ferry is attached (via many cables) to a pivot point high in the sky, fixed atop a strong pole that's in the center of the river.
When released, the ferry, with cars inside, swings across the river with elegance & speed.
At the other end, a latch
catches the ferry, cars drive out, and the next drive in. Also, there are restrooms for changing your pants.
Advantages:
1. Fast
2. Energy efficient. You're turning your potential energy into kinetic and then back into potential with little losses.
3. Fun
4. Far less material and labor to build than a traditional, boring suspension bridge.
Of course, you'd need a pretty strong pole, and some significant heights, but it's doable.
In case you don't have enough energy to get back to the other side, you swing for awhile and then a computer detects that and a propellor kicks in to give you that little boost you need.
(???) crude illustration
http://images.kodak...046312303_0_ALB.jpg
I'm not sure if you can see this, so please let me know if there are problems. [sophocles, Dec 20 2005, last modified Dec 21 2005]
This idea is almost baked - see the transporter bridge
http://en.wikipedia.../Transporter_bridge
Transporter Bridge [andrewbee, Apr 13 2010]
[link]
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I'd rather attach the swinging ferry car to
an A-frame than a pole and, as per Pave
above, you'd need to put a little energy in
every swing. I like it. [+] |
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Just be careful you don't turn into Wall Pancakes due to the acceleration. :) |
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Yep, we'd always need a little push/pull, but that would be likely less net energy expended than normal traffic on an old-style bridge. |
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EP: As for accelleration, it's just the same old "G"+/- one (0 at the start, which feels weird on your stomach, 2x at the bottom (down), and 0 at the end again). |
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Alternate method of construction: Rather than some high superstructure, consider a low counterbalanced pendulum swinging from the other direction. Of course, this is only an option for short or high spans. You lose efficiency fast if the pivot has to be under water. |
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[Worldgineer] I like yours. Having the pendulum in the water might be desirable for braking as the payload descends toward the far shore. |
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How about a platform on each side connected to the pole. Balance them out, then the pole rotates, swinging the loads across the river like two tetherballs. Have a banked offramp at the end and the cars could drive off without slowing down the mechanism! |
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Don't do a load of cars at a time. It takes a single car with an arrestor cable (or similar). Thus the energy of the car as it drives onto the platform is transferred rapidly to the platform. |
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You have a minimum drive on speed, and it ensures that the car makes it across with no additional energy input. |
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If the platform was moving fast enough and hit the other
shore with a resounding thud the inertia would unload
the cars in about a second. |
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How fast would the pendulum travel at its top speed? |
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Do you mean angular velocity, or linear velocity ? |
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The maximum value of both will occur at the bottom point of the swing, and can both be derived from the equations for Simple Harmonic Motion. |
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The linear velocity can be derived as the instantaneous velocity extrapolated from a tangent to the arc described by the pendulum. |
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