How Does Deformation Affect the Net Force Between Two Masses?

[anonymous99]

Homework Statement

Suppose you have two masses m1 and m2 with m2 on top of m1. I understand the normal force acting on m1 will be m1g+m2g and normal force on m2 will just be m2g but wanted to know, is this only true for rigid masses? If m1 was able to deform from the weight of m2 above it (like a trampoline for example), would a scale underneath m1 register less weight now?

Relevant Equations

Thanks

S

 

[haruspex]

Homework Statement:: Suppose you have two masses m1 and m2 with m2 on top of m1. I understand the normal force acting on m1 will be m1g+m2g and normal force on m2 will just be m2g but wanted to know, is this only true for rigid masses? If m1 was able to deform from the weight of m2 above it (like a trampoline for example), would a scale underneath m1 register less weight now?
Relevant Equations:: Thanks

S

Consider the vertical balance of forces on each mass. Can there be a net force on either?

 

[anonymous99]

I think there is for m1 because it wouldn't deform otherwise.

 

[haruspex]

I think there is for m1 because it wouldn't deform otherwise.

Equal and opposite forces are quite able to deform objects.
What does ΣF=ma tell you about the consequences of a net force?

 

[anonymous99]

Equal and opposite forces are quite able to deform objects.
What does ΣF=ma tell you about the consequences of a net force?

Well, there is a net force initially then while m1 deforms but once it's stopped deforming forces are balanced? I think it would be like with a trampoline. If someone stands on the trampoline, there's a net force that causes the ropes to sag downwards when you land from each jump and once the trampoline doesn't sag anymore, it will propel you back up.

 

[Lnewqban]

Even if mass 1 is not elastic and suffers a plastic deformation under the weight of mass 2, would a scale underneath mass 1 and 2 register less weight?

Tip: Weight force is only the result of the combination of mass and the acceleration of gravity.
Have any of those changed for mass 1?

 

[haruspex]

there is a net force initially then while m1 deforms but once it's stopped deforming forces are balanced?

Yes.
Does that answer your original question?