# Force needed to rotate 5000kg

1. Jul 29, 2011

### rahim

can someone help me?..

i have 5000kg suspended load..how do i calculate the force needed to rotate this load 90 deg. assuming perfect bearing?..thanks

2. Jul 29, 2011

### LostConjugate

Any amount of force. Once it starts rotating it will not stop assuming perfect bearing. I wish I had a perfect bearing.

3. Jul 29, 2011

### sophiecentaur

Go to deportment classes then. lol

4. Jul 29, 2011

### rahim

im just saying friction is neglected..thanks

5. Jul 29, 2011

### mrspeedybob

I was recently at a museum in Virginia that had a large stone globe in front of the building, I would estimate that it was 2 1/2 meters in diameter. The surface was very smooth and it was supported on a circular base. Water was forced up through the base which raised the globe slightly so that is was in physical contact with only water and air. While this in not a perfect bearing, it was a very good one. I could rotate the globe in any direction I wanted with 1 finger. The limiting factor for how fast I could accelerate the globe was not the strength of my finger but the lack of friction between my finger and the smooth, wet stone. Really I was only using about 1/4 of the strength of 1 finger. I inquired about the mass of the globe and was told that it weighs about 29 tons.

Here's a link to the museums website...
http://www.smv.org/exhibits.html [Broken]
One of the photo's is of the globe I am describing.

Last edited by a moderator: May 5, 2017
6. Jul 29, 2011

### Drakkith

Staff Emeritus
Any amount of force will eventually rotate it to 90 degrees. Similar to an object in space, the load will continue to move after any force is applied to it and then stopped. If you want to move it to 90 degrees in a specific timeframe, then that is different.

7. Jul 29, 2011

### dyce

being an automotive technician, I would use an foot pounds torque wrench.

8. Jul 29, 2011

### Drakkith

Staff Emeritus
The OP is asking the question and telling us that there is no friction or anything, it is just a suspended load. ANY force will move it to 90 degrees as long as there is no resistance to the motion. In reality we would have to take friction and other effects into account.

9. Jul 30, 2011

### dyce

it would need to be falling or floating in space in order to get it to rotate with almost 0 force. but floating in water would be "close" to 0 friction. this is if it is a smooth object. so yea youre right. but to get it to rotate under strength of earths gravity pulling on it, there would always be resistance.

10. Jul 30, 2011

### Drakkith

Staff Emeritus
Which is why we were all talking about a situation with no resistance!:tongue2:

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