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.
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.
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.
Score more than 80% marks and move ahead else stay back and read again!