Question

A sharp needle pierces the wood easily but not a blunt knife although the force applied on both is same.Why?

Answer 1

A sharp needle applies a great pressure on small surface area hence, it easily pierces in the wood.
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But a blunt knife applies pressure on a large surface area, so less pressure is exerted hence, it cannot cut easily and we have to apply more force.

Answer 2

A sharp needle pierces the wood easily but not a blunt knife although the force applied on both is same because the impulsive fore created by the sharp needle will be more than that of the blunt knife

as large amount of force will act over a small area the impulse created will be more which will pierce the wood easily