# Compressive force between objects

1. Sep 24, 2011

### Swalker

This is something I’ve been pondering for sometime and I’m looking to develop a better conceptual understanding so I look forward to any feedback that you can provide.

I have attached a drawing for clarity and a text description follows.

- Two objects of mass M1 and M2 are on a platform.
- Each object has a unique coefficient of friction (between the platform)
- The objects are physically connected to one another by a rigid load cell at location 2.
- The press moves in the x direction with a sinusoidal profile and it only moves for a -limited distance and it moves very slowly.
- The press applies force to M1 through a rigid load cell at location 1.
- A horizontal force is applied to M2 through a rigid load cell at location 3.
- The force F2 is significantly higher than any resistance imposed by frictional forces.
- The press readily moves the blocks and easily overcomes F2, drag, etc..

What I’m interested in discussing is:
1) Since the blocks are under compression are the forces at each of the load cells equal?
2) At one point the press goes against F2 and at another point they work together. How does that impact the relative values of the forces measured by each load cell?
Keep in mind the press moves very slowly. So, I’m simply wondering if the compressive forces between the blocks are equal even through the value of the forces vary.

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#### Attached Files:

• ###### press.JPG
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2. Sep 25, 2011

### gsal

The way I see it, the compression force is the same for both objects and, for as long as things are moving very very slowly and the press practically overcomes everything else, and effectively behaves like a wall...the compression force is simply F2 because is the smaller of the two forces...in other words, no matter how high the press pushes, things will stop compressing when the press force equals F2 and the object the produces F2 can no longer hold things in place and start moving back.

my 2 cents

3. Sep 25, 2011

### Swalker

Thanks for the feedback. You're thinking is along the same lines as mine. The system is under constant compression as long as the horizontal rate of change you of the press is slower than the acceleration that could arise front the applied force. Thanks for your feedback.