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Is it necessary that when an external force is applied on a solid body, it always gets deformed however small the deformation may be?

If the material is highly elastic like steel, even then there will be a deformation of the body for negligibly small forces.

Please explain theoretically i.e in terms of the structure of the solid (in terms of chemical bonds, potential energy curve etc) why this happens.

I think the deformation should start when a certain particular force is applied, because to disturb the packed lattice a certain force is required. But I am not sure, it is also possible that lattice gets instantaneously disturbed (eg for polymers). Is is really confusing.

peterh
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Matt
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1 Answers1

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No, it is not negligable.

The term "solid body" is an abstraction. In the reality, they don't exist, but there are bodies which are nearly solid and calculating them on this way significantly reduces the complexity of the calculations.

Most of them is a bound state of charged particles (electrons and nuclei). These interact

  • electromagnetically
  • by the Pauli-exclusion principle

There is nothing which would "fix" their distance to eachother. In the case of the "solid" bodies, these forces are in a configuration that to change their distance a little bit, means a high growth in the potential.

Side note: having really solid bodies (as in theory) would also contradict special relativity. If you apply a force to a solid body, the whole body would accelerate in the moment. It would mean that you sent information instantly in the whole volume of that body.

peterh
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  • What I am asking is to deform a nearly solid body is force of even very small magnitude sufficient it doesnt matter how big or small the strain is . And why ? – Matt Mar 04 '17 at 09:20
  • @RaghavSingal What I am answered that any small force will do this, there is a potential well between the particles. It is essentially a function showing the energy for the distance between the particles. In the normal state, the distance is on the minimum. If you pressure the body, it will change. The only difference between the nearly rigid objects and the others is that in their case the energy need grows very fast with the deviations from the minimal state. But, as far I know, this potential well can't have only perfectly horizontal and vertical lines. – peterh Mar 04 '17 at 10:37