# Torque on a "draw bridge"?

## Main Question or Discussion Point

Suppose I have a four foot high rectangular slab that weighs 100 pounds, and is hinged at the bottom. The slab is essentially a draw bridge. It is anchored at the by two chains on either side. A winch can lower and raise it. Suppose the slab is at 45 degree angle. How much torque is there in the chain? How about if it is at 60 degrees?.

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Bystander
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How much torque
Presumably you mean "tension" rather than "torque." Have you done the calculations? Are you asking how to do the calculations?

This is a practical application that I'm facing. It's been a long time since I did any physics. It would be interesting to know what the calculations are. I don't think it's tension. Torque is measured by force times lever arm.

OK, here's the application. See the image file. The clutch is rated at so much torque. Something like 70-110. If the torque produced by the slab is too great the clutch will slip, causing the slab to fall. The device on the floor will be mounted on a shutter of in an observatory. Actually, not on the shutter, but next to the shutter near the top.

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Bystander
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Whole buncha questions:
1) shutter opens inward, or outward;
2) chain/cable/whatever is pulling from frame to shutter where;
3) what sort of wind speeds are typical when opening/closing.

Torque on your winch motor is immaterial; you change sheave diameter to apply whatever you need.

1. outward
2. lowers and raises with winch, just like a drawbridge.
3. not used when there are strong winds.

I was wrong about where winch, motor, clutch. It is at the bottom.

Thanks for the interest. The technician I'm working with resolved issues I had.

Bystander