Massive rotating drum on bearings with friction

AI Thread Summary
The discussion revolves around analyzing the forces and friction involved in a rotating drum system with a suspended mass. The user is attempting to determine the coefficient of friction between the drum and its bearings, noting that the forces acting on the drum create a torque that influences its rotation. They express confusion about the role of friction, particularly how it produces torque and affects the normal force on the drum's center of mass. The user clarifies that the drum has a shaft with bearings inserted into it, leading to friction between the drum's inner surface and the bearings. The conversation emphasizes the need to incorporate all forces and torques in the calculations to accurately assess the system's dynamics.
erore
Messages
5
Reaction score
0
I came across the following example. I have a mass m' that is suspended from a massless rope which is wound around a drum of mass m. The radius of the drum is R. The drum is fixed on a shaft with bearings of radius r. I am supposed to determine coefficient of friction between the bearings and the drum but for now I am stuck with the forces diagram.
I created something like that:
attachment.php?attachmentid=51334&stc=1&d=1349007090.gif


In my solution I add a pair of forces of the same magnitude and opposite direction F^{T''} and F^{T'}. F^{T''} and F^{T} make a force couple which generates some momentum about the axis of the drum (which contributes to rotation motion). However, F^{T'} acts on the center of mass of the drum and adds up with gravitation force. Thus, the resulting force exerted by the drum on the bearing is bigger than if there was no m'. Consequently the friction is bigger too.

My question is whether this is correct. The solution I have only calculates the torque due to m' and does not introduce the force couple therefore it does not have the additional force on the center of mass and consequentially no additional item in the normal force and friction respectively.

I am also curious, the friction itself produces a torque, if my reasoning above is correct, it would create another force couple, giving rise yet to another force acting on the center of mass of the drum which could go on and on. This is confusing for me at the moment.
 

Attachments

  • drum.gif
    drum.gif
    12.4 KB · Views: 1,017
Last edited:
Physics news on Phys.org
Friction between what and what? Is the drum attached to something or in contact with something? That will somehow balance the force FT (otherwise the whole setup accelerates downwards).
 
I am sorry, the first paragraph was nonsense. I corrected. Basically, there is a hole in the middle of the drum of radius r and a shaft with bearings is inserted into that hole. The friction I mention is between the inner hole of the drum and the bearings.
 
Ah. I think I would draw the friction force at the upper side and in the other direction.
Afterwards, I would add variables for the angular acceleration and the force on the shaft and solve for those.
 

Thread '1:1 versus 2:1 Mechanical Advantage debate'

The rope is tied into the person (the load of 200 pounds) and the rope goes up from the person to a fixed pulley and back down to his hands. He hauls the rope to suspend himself in the air. What is the mechanical advantage of the system? The person will indeed only have to lift half of his body weight (roughly 100 pounds) because he now lessened the load by that same amount. This APPEARS to be a 2:1 because he can hold himself with half the force, but my question is: is that mechanical...
View full post »

Thread 'Newton's first law?'

Some physics textbook writer told me that Newton's first law applies only on bodies that feel no interactions at all. He said that if a body is on rest or moves in constant velocity, there is no external force acting on it. But I have heard another form of the law that says the net force acting on a body must be zero. This means there is interactions involved after all. So which one is correct?
View full post »
Thread 'Beam on an inclined plane'

Thread 'Beam on an inclined plane'

Hello! I have a question regarding a beam on an inclined plane. I was considering a beam resting on two supports attached to an inclined plane. I was almost sure that the lower support must be more loaded. My imagination about this problem is shown in the picture below. Here is how I wrote the condition of equilibrium forces: $$ \begin{cases} F_{g\parallel}=F_{t1}+F_{t2}, \\ F_{g\perp}=F_{r1}+F_{r2} \end{cases}. $$ On the other hand...
View full post »

Similar threads

B Calculating the torque needed to rotate a drum
Replies
4
Views
2K
Calculate Force Applied to Rope for Frictional Torque
Replies
2
Views
5K
B Static friction needed for rolling without slipping
Replies
4
Views
2K
I Torque required from powered roller to rotate cylinder
Replies
19
Views
2K
Motor Sizing for Wheel Endurance Testing
Replies
4
Views
2K
MIT 8.01: Unwinding Drum Problem
Replies
9
Views
2K
A Trying to understand couple stress in continua
Replies
6
Views
673
How Do You Calculate Component Forces in an Automotive Drum Brake?
Replies
3
Views
1K
Predicting Peak Displacement in Imbalanced Rotating Drum
Replies
35
Views
4K
Torque required to rotate a circular sector inside a drum
Replies
2
Views
3K

Hot Threads

Recent Insights

Back
Top