A sharp knife cuts better than a blunt one. Why?


The surface area of sharp edged knife is much less than the blunt edge. For the same total force applied, the effective force per unit area (or pressure) is more for the sharp edge than for the blunt edge. So sharp edge cuts better. 

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Define the terms thrust and pressure. State their SI units.


The total force acting on a body perpendicular to its surface is called thrust.

SI unit of thrust is newton (N).

Thrust acting per unit on the surface area is called pressure.


Pressure = Thrust
                   Area

The SI unit of pressure is Nm–2 or pascal (Pa).

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