Sunday, July 12, 2009

Friction force in this situation.

Click here to view model on you tube.

Well friction in this situation depends on various factor.

1. Load towards the center of pulley. ( The main and most important factor.)

2. Smoothness and lubrication at contact surfaces.

3. Contact area (if contact area is more, friction will be more)

4. Materials of pulley and stationary plate.

If one material is soft and other is hard friction will be less. I prefer pulley or cam is hard and stationary plate which is in yellow colour should be soft. Or you can put some rubber type material at contact area.

5 Curvature or half circular contact. If you use half circular contact instead of line contact friction will be less.

Here I will discuss the main factor load.

Load towards the center will generate opposite direction friction force. Which oppose the rotation of pulley. You might asked me what is the exact value of this opposite load or friction force. I already told you it depends on many factor.

Ok I put 200 kg load on pulleys and try to analysis the situation. You can see 200 kg load divide on two pulleys and apply on each pulley 100 kg load.

This 100 kg further divided in two part one is tangential and second is towards the center. This tangential part will help to rotate pulley and towards the center part will generate opposite frictional force.

Tangential force will be cos30* 100=86 kg because here alpha is 30`

Towards the center force will be sin30 * 100=50 kg.

How to calculate opposite friction force from the value of towards the center force which is 50 kg?

I give you one example just to get overall idea.

What is you car weight may be 1000 kg

Now put your car gear in neutral and try to push it from your hand. You can push it. Your hand has not more than 200 kg power but still you can push 1000 kg weight car with your hand on flat surface remember not on mountain.

I give you another example.

You can see we can slide 100 kg load with the help of 10 kg load. Remember we are not going to lift 100 kg. We just push it. So we have to apply only little more force than friction force.

So the basic thing is if the load towards the center is 50 kg then the opposite friction force ( which oppose the rotation of pulley) will not be more than 5 kg. But still we include some other parameter like your contact area is not curvature, you use less lubrication and make more contact area than considering all this parameter frictional opposite force will not me more than 10 kg.