Quick question on Normal force VS Acceleration

[aftershockzap]

My google skills have failed me and I am trying to remember something my professor told me about how forces interact and I figured, someone here will probably know.

Question:

Quick setup,

Object A is a huge wall at rest.

Object B is a smaller massed object with a velocity. (Say a car)

Object B crashes into Object A. Object B is damaged.

I (Think) know that the Normal force of the collision causes object B to experience rapid deceleration.

My question is this:

Is the damage on object B technically caused by the Normal force, Or the rapid deceleration?

[Seret]

I'm not sure it's a distinction worth making. The reaction force causes the deceleration. They're slightly different things. One is a force, the other is the action caused by that force. Deformation of B could be said to be caused by either or both.

[karolus10]

There is no distinction between "normal force" and "rapid deceleration". I would say that it's good example of inelastic collision.

When both bodies collide, main factors are their momentum and structural structure/strength (both car and wall is under same, but opposite force).

Edited August 4, 2013 by karolus10

[Yourself]

What technically causes the damage is a high stress compressive travelling through the materials. Objects don't being accelerating instantaneously when a force is applied to them, it takes time for that information to propagate through materials to the rest of the object. As a result you have different parts of each object accelerating at different rates and the interface between these different rates of acceleration is a wave.

[Ben 9072]

What technically causes the damage is a high stress compressive travelling through the materials. Objects don't being accelerating instantaneously when a force is applied to them, it takes time for that information to propagate through materials to the rest of the object. As a result you have different parts of each object accelerating at different rates and the interface between these different rates of acceleration is a wave.

Yourself is correct. It's the differing rates of acceleration that causes damage to the materials. In a slightly more detailed explanation, when the stress exerted in a local area due to the force differential from the acceleration causes a deformation (or strain) exceeding the material's yield strength, it will cause a permanent deformation. Prior to hitting the yield strength, the material can always return to its original shape. Exceeding that stress level, it will reach its ultimate strength and its rupture point, at which it will break/snap/etc, depending on the material. This diagram might be of help: https://en.wikipedia.org/wiki/File:Stress_v_strain_A36_2.svg Point 2 is the yield strength, point 1 is the ultimate strength, and point 3 is the rupture point.