Maharashtra BoardEnglish MediumSTD 12 SciencePhysicsMechanical Properties of Fluids2 Marks
Question
Why does a knife have a sharp edge or a needle has a sharp tip ?
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Answer
For a given force, the pressure over which the force is exerted depends inversely on the area of contact; smaller the area, greater the pressure.
For instance, a force applied to an area of $1 mm^2$ applies a pressure that is $100$ times as great as the same force applied to an area of $1 cm^2$.
The edge of a knife or the tip of a needle has a small area of contact.
That is why a sharp needle is able to puncture the skin when a small force is exerted, but applying the same force with a finger does not.
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