FLUID MIDTERMS
FLUID STATICS
ATOMS- rocks retains it shape since forces holding its atom togethter. Atoms in liquid are in contact but can slide over one another.
Water is example of liquid. Can flow but remains in open container because of forces between its atom.
Atoms in gas are separated by distances that are considerably larger than the size of the atoms themselves and they move out freely.
Plasma is composed of electrons, protons, and ions that are spaced apart and move freely.
FLUID- A fluid is a state of matter that yields to
Sideways or shearing forces. Liquids and
Gases are both fluids. Fluid statics is the
Physics of stationary fluids.
DENSITY
-Density is the mass per unit volume of a substance or object. In equation form,
Density is defined as P=m/v
Where the Greek letter ρ (rho) is the symbol for density, m is the mass, and V is the volume occupied by the substance. The SI unit of density is kg/m3
-Density also reveals something about the phase of
The matter and its substructure. Notice that the
Densities of liquids and solids are roughly
Comparable, consistent with the fact that their
Atoms are in close contact. The densities of gases are much less than those of
Liquids and solids, because the atoms in gases are
Separated by large amounts of empty space.
PRESSURE
-Pressure is defined as the force divided by the area perpendicular to the force over which the force is applied, or P=F/A
-The SI unit for pressure is the pascal, 1Pa =1N/m2
-In addition to the pascal, there are many other units for pressure that are in common use. In meteorology, atmospheric pressure is often described in units of millibar (mb), where 100 mb =1×105 Pa
-Pounds per square inch (lb/in2 or psi) is still sometimes used as a measure of tire pressure, and millimeters of mercury (mm Hg) is still often used in the measurement of blood pressure.
PRESSURE UNDER WATER
-Area is therefore inversely proportional to pressure. Force on the other hand is directly proportional
to pressure. Meaning as you increase force, the greater pressure is attained, and vice versa.
- if we are looking for the force acting on the body of a scuba diver, we can get his force by F = mg
EQUALIZATION- a condition of fluid pressure equilibrium between two production zones. Pressure equalization occurs when fluid in a reservoir flows from a zone at high pressure to the zone at low pressure.
ATMOSPHERIC PRESSURE
-Atmospheric Pressure is another example of pressure due to weight of a fluid, in this case due to the weight of air above a given height. The atmospheric pressure at the Earth’s surface varies a little due to the large-scale flow of the atmosphere induced by the Earth’s
rotation (this creates weather “highs” and “lows”). However, the average pressure at sea
level is given by the standard atmospheric pressure P(atm) , measured to be 1 atmosphere (atm)= P(atm) = 1.01 x 10^5 N/m^2 = 101 kPa
-This relationship means that, on average, at sea level, a column of air above of the Earth’s surface
has a weight of 1.01 x 10^5 N, equivalent to 1 atm.
PASCAL’S PRINCIPLE
-Pascals’ Principle states that pressure
applied to an enclosed liquid is transmitted uniformly in all directions.
P1 = Pressure on small piston
P2= Pressure on big piston
F1 = input force
A1 = small piston area
F2 = output force
A2 = big piston area
Application of Pascal’s Principle
1. Hydraulic Lift - use a hydraulic cylinder system to lift, move, and position heavy loads. While
their designs vary depending on the intended application, all hydraulic lifts function using the
same basic components: A hydraulic cylinder enclosing a piston. A reservoir for oil storage. A
pump for generating fluid energy.
2. Hydraulic Brakes – is an arrangement of braking mechanism which uses brake fluid, typically
containing glycol ethers or diethylene glycol, to transfer pressure from the controlling
mechanism to the braking mechanism.
ARCHIMEDES’ PRINCIPLE
-ARCHIMEDES- physicist, mathematician, astronomer, inventor. Known for achievement “Eureka”
-Buoyant Force –the net upward force exerted in an object that is partially or wholly submerged in a
fluid. Symbol: FB Unit: Newton (N)
Applications of Buoyancy
● Submarine lowers by giving water access to the balance tank with the goal that its weight
gets more prominent than the buoyant force.
● Boat is developed as it were with the goal that the shape is empty, to make the general
density of the ship less than the ocean water.
● Hot air balloons, it heats the air inside the balloon, wherein hot air rises and is lighter than
the cold air outside. And of course, as the air inside the balloon cools down, the hot air
balloon slowly goes down as well.
● To fishes, Archimedes’ principle is the one behind how fishes are able to go up in the water
surface. They fill their swim bladder with gases, from the body, the gases diffuse to the
bladder, making their body lighter, thus, easier to go up.
KEY CONCEPTS
● Having higher density means more mass hence more weight in the same volume.
● An object floats if its specific gravity is less than 1, and sinks if the specific gravity is more than.
● An increase in mass with a constant volume will cause the object to sink in water.
● An increase in volume with a constant mass will cause the object to float on water.
● The buoyant force on an object is equal to the weight of the fluid displaced.
-If FB (buoyant force) is greater than the wobj (weight of the object), the object will float.
-If FB is less than the wobj the object will sink.
If FB equal to the wobj the object is suspended at that depth.
Density and the Archimedes’ Principle
-The average density of an object determines whether it floats.
pobj < pfl it will float
pobj > pfl it will sink
Specific Gravity –the ratio of the density of an object to a fluid (usually water).
Specific gravity or Relative Density (RD)
SURFACE TENSION AND CAPILLARY ACTION
Cohesive Force
- The attraction between atoms and molecules of the same type.
- E.g., Water, Mercury
Adhesive Force
- The attraction between atoms and molecules of different type.
- E.g., Rain drop sliding/clinging to our skin.
SURFACE TENSION
- The liquid’s tendency to shrink or contract into the minimum surface area possible because
of cohesive forces between molecules.
- The inward force pulls molecule to reduce the surface area.
Formula: Y=F/d
SI Unit: N/m (Newton per meter)
y: surface tension of the liquid
F: force
d/L: length
THE GAUGE PRESSURE, P
P = 4y/r
Where: SI Unit: Pa (Pascal)
P: gauge pressure
Y: surface tension
R: radius
Pressure inside a bubble is greatest when the bubble is the smallest.
Contact Angle (Ꝋ) refers to the tangent to the liquid surface and the surface where the liquid is.
The larger the Ꝋ, the larger the cohesive strength relative to adhesive force, thus forming a droplet.
The smaller the Ꝋ, the smaller the relative strength and the adhesive force flattens the drop.
CAPILLARY ACTION
- The liquid’s tendency to raise or suppress in a tube without an external force like gravity.
- Commonly called as capillary motion, capillarity or wicking.
Meniscus – the curved surface of a fluid in a tube.
Capillarity in tube is affected by the liquid’s weight
Where: SI Unit:
h = elevation of the liquid m
T/y = surface tension N/m
Ꝋ = contact angle rad (radians)
p = density of the liquid kg/m
g = acceleration due to gravity m/s2
r = radius of capillary tube m
APPLICATIONS OF SURFACE TENSION AND CAPILLARITY IN REAL LIFE
● Small insects such as the water strider can walk on the surface of the water because their
weight is very less so they can’t penetrate the water.
● Disinfectants are mainly the solution of low surface tension so that when we use them in
the field they can float on the water and spread out on the cells to destroy them.
● Soaps and detergents also work on the basis of surface tension. They lower the surface
tension of the water so that the soaps and detergents easily soak into the pores and holes.
● The water bubbles are round because the surface tension of water provides the tension to
form the bubble with the water and the surface tension minimizes the bubble into spherical
shapes.
● Surface tension changes in biological phenomena can determine various diseases in the
human body.
● Surface tension is an important factor in industrial processes. In all the industrial plants the
R&D departments use the surface tension phenomena to improve the quality of the
products.
● Surface tension is also important for characterization for food, pharmaceutical and
packaging products.
● Capillary action is the process that plants use to pull water and mineral up from the ground.
It is the movement of liquid along a surface of a solid caused by the attraction of molecules
of the liquid to the molecules of the solid. The molecules of the water (liquid) are attracted
to the molecules inside the stem similar to capillary action of water in a glass tube.
● The rise of Kerosene in the wick lantern
● Sucking of ink by the blotting paper
● The rise of ink in the nib of a fountain pen
● Sucking of water by the towel.
PRESSURES IN THE BODY
Systole
- The phase of the heartbeat when the heart muscle contracts and pumps blood from the
chambers into the arteries.
Diastole
- The phase of the heartbeat when the heart muscle relaxes and allows the chambers to be
filled with blood.
Pressure
- The perpendicular force per unit area or the stress to a point within a confined fluid.
Atherosclerosis
- Thickening or hardening of arteries caused by build-up of plaque in the inner lining of an
artery.
Glaucoma
- Group of eye conditions that damaged the optic nerve. This is the health for good vision.
mm Hg
- Millimetres of mercury, unit for pressure.
- Equivalent to 133.3 Pa
Aqueous humor
- fluid produced by the eye and provides nutrition to the eye as well as maintain its
pressurized shape.
Blood Pressure
- It is the pressure of blood pushing against the walls of the arteries. A healthy individual can
have a systolic reading of 90-120 mmHg and diastolic reading of 60-80 mmHg. Common
arterial blood pressure measurements typically produce values of 120 mmHg and 80
mmHg. So if you know how to use aneroid sphygmomanometer, this is the normal blood
pressure for adults.
-blood flows from high pressure to low pressure. From
the left atrium, blood flows to the aorta with a pressure of 120 mmHg. It will go down until
it goes through the arteries, veins, right ventricle and right atrium with a pressure of 4
mmHg. During systole, it is the highest where the heart contracts and pumps blood from
the chambers into the arteries, while the diastole which is the lowest is when the heart
relaxes and allows the chambers to be filled with blood.
What affects blood pressure to have implications?
⮚ Substances present in the blood
The blood contains carries several substances such as red blood cells, white
blood cells, oxygen, nutrients, proteins, cholesterol, and wastes that are transported
throughout the body. A thick blood because of the substances present will require
greater pressure, and thus, the pump is required to pump harder.
⮚ High Salt Diet
A high salt diet increases blood volume because it promotes water retention. An
increase in volume needs greater pressure to force the blood to continue moving.
⮚ Stress
Release of epinephrine and norepinephrine hormones because of stress
increases resistance making the blood less fluid that leads to a greater pressure that the
blood needs.
⮚ High blood pressure (hypertension)
Having a high blood pressure injures the arterial walls. When it’s injured, white
blood cells are collected on the injured part. Other substances of the blood have the
potential to clump on the injured part as well, thus leading to Arthrosclerosis that makes
arteries get swollen and become narrow. This can stop or resist blood flow leading to
heart attack, stroke, and death of muscle cells.
Eye Pressure
-Intraocular pressure (IOP) keeps the shape of the eye spherical which is filled with fluid.
The normal IOP is ranging from 12 to 24 mmHg.
-How pressure affects the eye?
In normal cases, the eye secretes a fluid – the aqueous humor – that continuously flows.
The rate of secretion is balance by the rate of drainage of that fluid. When the posterior chamber
or the space between the iris and the lens is clogged or completely blocked, the fluid will rise
up through the pupil up to the anterior chamber that makes the pressure within the eye increase
and leads to glaucoma or the damage of the optic nerve.
LUNG PRESSURE
Normal pulmonary artery pressue is 8-20 mmHg. If 25 mmhg and 30 mmhg, it is considered to be pulmonary hypertension due to abnormally high reading.
As you can see here in the image, when we breathe in, the chest or the lungs expand, and also the pressure decreases. When we breathe out, our lungs and chest contracts and the pressure increases. Pressure is equal to force over area. The pressure is inversely proportional to the area. A decrease in area just like when the chest contracts because we breathe out, the
pressure increases, and vice versa.