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**Impact .... what? Force or Energy?**

I have a question, about what to calculate if calculating whether an immovable object (a wall for example) will break or not after an impact of another object into it. What should I calculate, the force of the impact or the kinetic energy of the impacting object?

I know that kinetic energy is calculated as E = 1/2 m v

^{2}and that impact force is calculated as F = m v / t (duration of impact). But which one should I calculate? I used to think that impact force should be calculated and from that I calculate the internal stress of the struck object, but if this is true, why are they calculating absorbed energy in izod and charpy tests?

Thank you for your time

Aragorn49