Question

A needle is required for stitching cloth. We use a knife for cutting fruit. If the tip of a needle or the edge of a knife becomes blunt, then the needle does not penetrate the cloth and the knife does not cut into the fruit. Why is this so?

Answer 1

A sharp needle or knife has a very small pointed or cutting surface, so the applied force acts on a smaller area and produces greater pressure. Therefore, it can easily penetrate cloth or cut fruit.

When the needle tip or knife edge becomes blunt, the same force acts over a larger area, so the pressure becomes less. Hence, the needle does not pierce the cloth easily, and the knife does not cut the fruit properly.