Pressure

For the same force, a smaller area gives greater pressure. Liquids and gases also press on the walls of their container, and the air around us presses on everything, which we call atmospheric pressure.

In real life: A sharp knife cuts easily because its thin edge puts the force onto a very small area, giving high pressure.

Worked example 1

Question. A force of 100 N acts on an area of 2 m². Find the pressure.

Answer: The pressure is 50 pascals (Pa).

Winds and lightning

Lightning can strike buildings and harm life and property. A lightning conductor, a metal rod joined to the earth, safely carries the charge to the ground. The India Meteorological Department watches storms and cyclones and warns people.

In real life: During a storm, standing under a tall tree is dangerous, while a building with a lightning conductor is far safer.

Worked example 2

Question. Why does a sharp needle pierce cloth easily?

Answer: Its tiny tip area makes the pressure very high, so it pierces easily.

Worked example 3

Question. How does a lightning conductor protect a building?

Answer: It carries the lightning’s charge safely down to the earth, away from the building.