Question

If someone presses a pointed needle against your skin, you are hurt. But if someone presses a rod against your skin with the same force, you easily tolerate. Explain.

Answer 1

By the knowledge of the Pressure, we can say that Pressure is inversely proportional to the Area when the Force is constant.

∵ Pressure =- Force/Area.

Now, think in the manner as given in the question using this formula.

We will conclude that if someone press our skin with a pointed niddle, it will be having the less area of the cross-section.

∴ Pressure will be more, since they are inversely related.

∴ We will be hurted.

But the same problem will get reversed if someone press with a rod, because that is having a large area of the cross-section, thus it will have less pressure than that of the niddle.

Hope it helps.

Answer 2

As we know
P = F/A
Hence if area of cross section is small then a small force will create larger pressure.
Thus us the main reasin with respect to needle and rod
Area of cross section of needle is smaller compared to rod hence needle hurts more than the rod.