lets discuss another important concept in,
fluid statics that is pressure at different
levels in a liquid. when we talk about a static
fluid we can simply state a point. in a static
fluid. its free surface. is always . normal
to the. effective acceleration. acting on
the fluid. like for an example we can simply
state if we are having a container in which
a liquid is filled. we can simply state the
effective acceleration acting on it will be
in downward direction that is g, and the free
surface of liquid will always exist in a direction
normal to this g and based on this we can
also state one more thing, all the points
in the free surface must be at equal pressure
or we can say pressure at all these points
must be equal, as the fluid is in, iquilibrium
. or we can simply state , all the layers,
of this fluid which are, parallel to the free
surface of liquid . will also have equal pressure
at all points in a layer. Like if we consider
a point x, a point y and a point z here we
can simply state pressure at x is equal to
, pressure at point y is equal to pressure
at point z. so always remember that . in a
layer. of fluid. parallel to. free surface
. of fluid. pressure. remain same, for all
points. and it is not only for , such a simple
situation which i have taken it is applicable
for all kind situation like . say we are given
with a cone-icle flask. and in which, you
can say, we connect a tube . and the size
of tube and shape of tube is varying like
this. and through this tube a funnel is connected
and, in the funnel we pour some liquid. and
say liquid is filled up to this level. in
the tube, as well as, the cone-icle flask
is completely filled. in this situation if
i take a horizontal layer , and there are
three points in the liquid , ay b and c. which
are on the same horizontal level which is
perpendicular to effective gravity acting
on it. and we can simply state as all the
three points . are , in a fluid body . which
is a single liquid so we can always write
p-ay is equal to p-b is equal to p-c. but
this is not the case , when two or more liquids
are mixed. lets consider one more situation
based on that. in sequence let us discuss
a situation when in a u tube there are two
immiscible liquids which are filled. this
is liquid of density ro-one this is the liquid
of density ro-two. and ro-one is more then
ro-two because of which we can state as pressure
, due to the liquid-one, is more at the bottom
it is displace the second liquid slightly
upward. now in this situation say if we consider
, few different points like say this is a
point ay and this is point b. at the same
level and both ay and b exist . within the
fluid body of liquid when we can write that
pressure at point ay must be equal to pressure
at point b. because they lie on same horizontal
layer which is normal to, the effective gravity
g, but if we consider a point c which is at
the top of this liquid . and at the same level
we consider a point d in the other liquid.
although they are also at the same level,
but still we can state that p-c is not equal
to p-d as. the two liquids are different,
and the points are lying on the same, horizontal
surface which is normal to g. still this is
not be applicable because liquids, the two
liquids are different. and this can be directly
seen that as point c is at the top of this
liquid, pressure at c can be taken as p-atmospheric
. where as if we talk about pressure at point
d, it’ll be p-atmospheric plus some value
so it’ll be more then p-atmospheric so we
can directly state there is no direct co-relation
between, pressure at c and pressure at d.
so always remember when we talk about a single
liquid we can always use pressure at all points,
in a layer which is normal to effective acceleration
acting on it , will remain constant.
