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Using pressure, force and surface area to test the sharpness of a knife
The presenter wants to know if two knives are of identical sharpness, so she sets up an experiment to apply the same force to the knives to cut an apple each. One kilogram masses are gradually added to increase the force on each knife. Eventually, one knife cuts the apple with less force than the other. The presenter questions why this might be and talks about force, pressure and surface area of the knife blade.
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