Question

Tools meant for cutting and piercing have sharp edges.give reason

Answer 1

Sharp edges are meant for cutting and piercing always because the reason behind this is sharp edges are having lesser contact force so they force will be more so they would cut or even piercing any thing easily. So they are meant for cutting. 

Answer 2

Tools meant for cutting and piercing have sharp edges because they have less area of contact and therefore can apply more pressure while cutting and the cutting becomes easier

as the surface area is less more pressure will be applied on the object