Thrust and Pressure Video Lecture - Class 9

trust and pressure when you fix a poster
on a bulletin board you need to press
drawing pins with your thumb you apply
force on the surface area of the head of
the pin which is directly perpendicular
to the surface area of the board the
force acting on an object perpendicular
to the surface is called as trust trust
is a vector quantity the unit of trust
is same as the unit of force that is
Newton a body always exerts the force
equal to its weight on any surface
supporting it
the effect of this force on the surface
depends on the area on which it is
spread
that is why when you stand on a loose
sand your feed goes deep into the sand
but on the other hand if you lie down on
the sand your body does not go that deep
into the sand in both the cases the
force exerted on the sand is the weight
of the body yet its effect is different
in both the cases why is that so when
you stand on the loose sand the force
that is the weight of your body is
acting on an area equal to the area of
your feet when you lie down the same
force acts on an area equal to the
contact area of your whole body which is
obviously larger than the area of your
feet we see that the effect of force
thrust of the same magnitude on
different areas is different lesser the
area more the effect of the trust
that means the effect of trust depends
on the area on which it acts the
physical quantity that explains the
dependence of trust on area is pressure
the trust acting on unit area of the
surface is called as pressure
substituting the SI unit of the trust
and area in the equation area of
pressure is capital n divided by small M
raised to the power two in the honor of
scientist Blaise Pascal the SI unit of
pressure is called as Pascal denoted by
P a the same force acting on a smaller
area exerts a larger pressure and a
smaller pressure on a larger area this
is the reason why Anil has a pointed tip
knives have sharp edges and buildings
have wide foundations