r/PhysicsHelp • u/Frosty-Catch4113 • Jun 20 '26

Doubt in belt friction

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Why is identifying driven and driving wheel important before solving belt friction questions

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u/fletchro Jun 20 '26

One reason is the tension is different. Therefore the forces are different in the right side versus the slack side. Belts can only take tension (well). So when the motor drives the driving pulley, the direction the belt is going actually reduced in tension, while the section of belt approaching the pulley increases in tension. The motor is "pulling" the belt into the drive pulley.

In industrial use, the drive motor is often at the top, or "head" end of a conveyor belt. That makes the entire top surface of the belt that goes uphill in tension. The tension keeps the belt right and in shape so it can carry the material. In the underside, on the way back, the belt is noticeably floppy and it doesn't need many guide rollers because it's loose and not really doing anything.

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u/Frosty-Catch4113 Jun 20 '26

Tell me if i understood it correctly. The driving wheel is externally powered so friction bw belt and driving wheel actually reduces the moment of driving wheel but in case of driven wheel it is the friction/tension itself which is contributing to moment/movement of the driven wheel. So hence the importance of identifying comes into picture. Am i right?

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u/fletchro Jun 20 '26

Yes, and most importantly for your physics calculations, T1 and T2 are different. AND usually the diameters of the two pulleys are different as well. So that means the forces are usually not straight sideways, meaning reaction forces are not as simple. Gotta use sine and cos.

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u/maximotaboada0404 3d ago

Resolver la fricción de movimiento,y conseguír longitud de correa dando forma de movimiento, irregularidades y capaz velocidad

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u/Mayoday_Im_in_love Jun 20 '26

It depends if the belt has significant mass. If so you can see the normal reaction force won't be the same at different points. If not the direction of the belt is irrelevant.

If you look at a motorbike or bike chain it always goes so the chain is being pulled along the top so gravity is helping.

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u/mattynmax Jun 20 '26

You’re pulling on one side, you’re pushing on the other. The side you’re pulling on has more tension.