I am carrying out a shake table test on a model that has two halves that rest one on top of the other. Two accelerometers are attached, one at the bottom (table) of the model and one at the top (system). The two sections are not rigidly attached, only the frictional forces between the two exist.

I have plotted the acceleration/time graphs of the test and have discovered that the acceleration on top is larger than the acceleration on the bottom (no real surprise).

What does this mean exactly for this model?

Is the top almost moving out of phase with the bottom?

Regards.