Direction of friction between disks

In summary, the problem involves two disks, D and E, where D is rotating at a constant clockwise angular velocity of 30 and E has a weight of 60 lb and is initially at rest. The goal is to find the time it takes for E to reach the same angular velocity as D, taking into account a coefficient of kinetic friction of 0.3 between the two disks. The relevant equation for solving this problem is the summation of forces and moments. The direction of friction is initially confusing, but it is found that the friction points to the left when isolating disk D and to the right when isolating disk E, which is correct.
  • #1
edsoneicc
11
0

Homework Statement


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Disk D turns with a constant clockwise angular
velocity of 30 . Disk E has a weight of 60 lb and is
initially at rest when it is brought into contact with D.
Determine the time required for disk E to attain the same
angular velocity as disk D. The coefficient of kinetic
friction between the two disks is 0.3 . Neglect the
weight of bar BC.

2. Relevant equation
Summation of forces and moments.

The Attempt at a Solution


I am confused with the direction of friction. In my calculations, the friction points to the left because the velocity where the disk meets points to the right; which resulted to a wrong answer. However, the correct free body diagram is shown above.
 
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  • #2
edsoneicc said:
the friction points to the left
That is the force that "what" exerts on "what else?" And what is the reaction force to that?
 
  • #3
So when I isolate disk D, the friction points to the left to counter the clockwise motion, and when I isolate disk E, it now points to the right. Is this right?
 
  • #4
Yes.
 
  • Like
Likes edsoneicc
  • #5
Thanks!
 

1. What is the direction of friction between two disks?

The direction of friction between two disks depends on the direction in which they are moving relative to each other. If the disks are moving in opposite directions, the frictional force will act in the opposite direction of the motion of the disks. If the disks are moving in the same direction, the frictional force will act in the same direction as the motion of the disks.

2. How does the direction of friction affect the movement of the disks?

The direction of friction plays a crucial role in determining the movement of the disks. If the frictional force is acting in the opposite direction of the motion, it will slow down or stop the movement of the disks. If the frictional force is acting in the same direction as the motion, it will help to maintain the movement of the disks.

3. Can the direction of friction between two disks change?

Yes, the direction of friction between two disks can change. It depends on the direction in which the disks are moving relative to each other. If the direction of movement changes, the direction of friction will also change accordingly.

4. How does the surface material of the disks affect the direction of friction?

The surface material of the disks can have an impact on the direction of friction. If the disks have a rough surface, the frictional force will act in the opposite direction of motion, making it harder to move. On the other hand, if the disks have a smooth surface, the frictional force will act in the same direction as the motion, making it easier to move.

5. Is the direction of friction the same for all types of disks?

No, the direction of friction can vary for different types of disks. It depends on various factors such as the surface material, the weight of the disks, and the direction of movement. Therefore, the direction of friction can be different for different types of disks.

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