Question

Why does a dull hypodermic needle hurt more than a sharp one?

Short answer

A dull hypodermic needle has more surface area than a sharp needle so more force need to be applied.

Step-by-step solution

Finding difference between dull hypodermic needle and sharp needle

The surface area of a sharp needle is small compared to that of a dull hypodermic needle. Since pressure is the force applied per unit area, pressure will be more acute because of this, as pressure and area are inversely related.

Explaining the reason behind the larger pain caused by dull hypodermic needle

Inserting a dull needle is more painful than inserting a sharp one. Because pressure will be less in a dull needle, more force will have to be applied to puncture the skin. In the case of a sharp needle, it will puncture easily.

So, the larger surface area of a dull hypodermic needle hurts more than a sharper needle.