Mechanical Properties of Fluids Flashcards
what is pressure
it is the normal force acting per unit area
unit: Nm-2/ Pa
Dimensions ML-1T-2
It is a scalar quantity
what is mass density
(ii) relative density
it is the mass per unit volume
scalar
unit: kgm-3
ML-3
A
liquid is largely incompressible and its density
is therefore, nearly constant at all pressures.
Gases, on the other hand exhibit a large
variation in densities with pressure
The density of water at 4oC (277 K) is
1.0 × 103 kg m–3. The relative density of a
substance is the ratio of its density to the
density of water at 4oC. It is a dimensionless
positive scalar quantity.
what is atmospheric pressure
pressure exerted by the atmopshere at sea level is c/a atmospheric pressure
- another unit of pressure(atm)
1 atm= 1.013 x 10^5 Pa
state pascals law
the pressure applied at any point on a continuous fluid at equilibirum is equally transmitted to all pother points of the fluid.
what is the hydrostatic paradox
The pressure at a certain horizontal level in the fluid is proportional to the vertical distance to the surface of the fluid. It does not depend upon the amount of fluid present in the vessel.
explain the working of a mercury barometer
A long glass tube closed
at one end and filled with mercury is inverted
into a trough of mercury as shown in Fig.10.5 (a).
This device is known as mercury barometer. The
space above the mercury column in the tube
contains only mercury vapour whose pressure
P is so small that it may be neglected. ( so only pressure at B is rho hg )The
pressure inside the column at point A must
equal the pressure at point B, which is at the
same level. Pressure at B = atmospheric
pressure = Pa
Pa = ρgh
In the experiment it is found that the mercury
column in the barometer has a height of about
76 cm at sea level equivalent to one atmosphere
(1 atm)
other units of pressure
1 torr = 133 Pa.
The mm of Hg and torr are used in medicine
and physiology. In meteorology, a common unit
is the bar and millibar.
1 bar = 10^5Pa
what is a u tube manometer?
An open-tube manometer is a useful
instrument for measuring pressure differences.
It consists of a U-tube containing a suitable
liquid i.e. a low density liquid (such as oil) for
measuring small pressure differences and a
high density liquid (such as mercury) for large
pressure differences. One end of the tube is open
to the atmosphere and other end is connected
to the system whose pressure we want to
measure.
The pressure P at A
is equal to pressure at point B. What we
normally measure is the gauge pressure, which
is P − Po.
Pa = Pb
Pa=ρgh+ Po
Pa-Po=ρgh
this is guage pressure
explain the mechanism of action of hydraulic lift
A piston of small
cross section A1
is used to exert a force F1
directly on the liquid. The pressure P =
1
1
F
A
is
transmitted throughout the liquid to the larger
cylinder attached with a larger piston of area A2
,
which results in an upward force of P × A2
.
Therefore, the piston is capable of supporting a
large force (large weight of, say a car, or a truck,
placed on the platform) F2 = PA2 =
1 2
1
F A
A
. By
changing the force at A1
, the platform can be moved up or down. Thus, the applied force has
been increased by a factor of 2
1
A
A
and this factor
is the mechanical advantage of the device.
what is the working of hydraulic break
The working of a break is based on Pascal’s Law. When the pedal is pressed, the lever system operates. The master piston is pushed inwards into the master cylinder. Hence there is a pressure applied at that point to fluid ( brake oil). This is equally transmitted to the larger pistons, acc pascals law. As a result these bigger pistons move outward, causing hte breakshoes to move away from each other, retarding the motion of car.
What is gauge pressure
The difference between the total pressure at that point and atmospheric pressure is called gauge pressure
