Static friction rotating discs

In summary, the conversation discusses the concept of static rotation torque and the calculation for determining the torque required to start rotation. The scenario of inserting a third disc and its effect on the torque is also mentioned. The conclusion is that the torque required for the middle disc would be the sum of the two contact faces, which is 400Nm.
  • #1
RichyRich85
2
0
Hi everyone

This is my first post on the forum. I work in engineering and use this forum to answer questions from time to time.

I am looking for confirmation of my understanding of static rotation torque (not something I deal with in day to day work).

Imagine 2 identical discs or washers that can rotate. The i/d is 0.095m and o/d is 0.105m. The coefficient of friction is 0.4. They are held together by an invisible force of 10kN. I believe the torque required to start rotation is (coefficient of friction x radius x force) 0.4x0.05×10000=200Nm

Next scenario: A third identical disc is inserted between the other two, and the two outer discs are unable to rotate. The same invisible 10kN force is applied on both of the outer discs. Would the torque required to rotate the middle disc be the same 200Nm, or would it be the sum of the 2 contact faces, I.e. 400Nm. I believe the latter, but just wanted to check.

Thanks in advance.
Richard
 
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  • #2
Yes, the two torque resistances will add.
 
  • #3
haruspex said:
Yes, the two torque resistances will add.

Thank you haruspex. I appreciate the feedback.
 

1. What is static friction in rotating discs?

Static friction in rotating discs refers to the force that acts between two surfaces in contact with each other, preventing them from sliding or moving relative to each other. In the case of rotating discs, it is the force that allows the disc to maintain its rotation without slipping or accelerating.

2. How is static friction different from kinetic friction in rotating discs?

Static friction is the force that opposes the initial motion of the rotating disc, while kinetic friction is the force that opposes the motion of the disc once it is already in motion. In other words, static friction is the force that keeps the disc from slipping, while kinetic friction is the force that slows down the disc's rotation.

3. What factors affect the magnitude of static friction in rotating discs?

The magnitude of static friction in rotating discs is affected by the coefficient of static friction, the normal force acting on the disc, and the surface characteristics of the disc and the object it is in contact with. A higher coefficient of static friction, a greater normal force, and rougher surface textures can all increase the magnitude of static friction.

4. Can the direction of static friction in rotating discs change?

Yes, the direction of static friction in rotating discs can change depending on the direction of the applied force. If the applied force is in the same direction as the disc's rotation, the static friction will act in the opposite direction, preventing the disc from slipping. However, if the applied force is in the opposite direction of the disc's rotation, the static friction will act in the same direction, causing the disc to slow down or stop.

5. How does the radius of the rotating disc affect static friction?

The radius of the rotating disc can affect the magnitude of static friction. A larger radius means a longer distance between the point of contact and the axis of rotation, resulting in a greater torque and a stronger static friction force. This is why larger discs tend to have a higher resistance to slipping compared to smaller discs.

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