Chapter 24: FORCE


This is either contact [friction, muscular] or non contact [magnetic, electrostatic, gravitational, pressure]


Pressure is inversely related to area. So smaller the area, larger the pressure for the same force.

Pressure and its real applications

E.g. Nail is easily pushed into wood from its pointed end than its head, tools for cutting have a sharp edge, shoulder bags have broad straps, and porters carrying heavy loads wrap a cloth on their head.

A large wooden plank placed on top of the circus performer keeps his ribs from breaking when an elephant steps on him.

All above activities regulate pressure by changing the surface area.

Suits of astronauts are filed with air to counter the pressure exerted by the body otherwise their blood vessels would burst as there no pressure on the moon.

At high altitudes, pressure is low so liquids boil at low temperature. Hence we use pressure cookers to cook.

In autoclaves to sterilize medical instruments, waters boiling point is increased by putting higher pressure on it.

Pressure by liquids

Liquids also exert equal pressure at the same depth. Air also exerts a great pressure on organisms but our body counters the pressure so we don’t feel anything.

Liquids are treated as in-compressible, whenever pressure is applied on any part of a liquid it is transmitted in all directions equally and undiminished. This principle is used in hydraulic lifts and brakes.


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