3A7 Basic Fluid Mechanics Flashcards
Explain basic fluid mechanics, including the role of fluid statics and fluid dynamics.
What are the main characteristics of a fluid?
- No fixed shape
- Can flow
- Particles move freely
A fluid includes liquids and gases. Key properties of fluids include viscosity, density, compressibility, and pressure.
Define
Fluid mechanics
Branch of physics that studies the behavior of fluids (liquids and gases) in motion and at rest.
Fluid mechanics combines principles of mechanics, thermodynamics, and material science.
True or False
Both liquids and gases are considered fluids.
True
Fluids are substances that flow and adapt to the shape of their container.
Fill in the blanks:
Fluid ______ studies fluids at rest, while fluid ______ studies fluids in motion.
statics; dynamics
Fluid statics focuses on pressure and buoyancy, while dynamics examines flow behavior.
Explain why fluid mechanics is important in engineering.
They help design systems like pipelines, hydraulic machines, and aircraft, ensuring they function efficiently and safely.
Applications include aerodynamics, hydraulics, and even weather prediction.
True or False:
An object floats if its weight is less than the buoyant force.
True
Floating objects displace an amount of fluid equal to their weight.
Fill in the blank:
The pressure exerted by a fluid increases with ______.
depth
Hydrostatic pressure increases due to the weight of the fluid above.
Why does a dam have a thicker base than top?
To withstand higher pressure at greater depths.
Hydrostatic pressure is proportional to depth and density of the fluid.
Define:
hydrostatic pressure
It is the pressure exerted by a fluid at rest due to its weight.
Calculated as P=ρgh, where ρ is density, g is gravity, and h is depth.
What is the hydrostatic pressure equation?
P = ρgh
This equation can also be written as P = ρgd + Patm, where ρ is the density, g is the gravitational constant, and h is the depth.
What is the SI unit for hydrostatic pressure?
Pascals (Pa), equivalent to N/m².
Pressure is defined as force divided by area.
Define:
gauge pressure
The additional pressure exerted on an object or fluid above atmospheric pressure.
Absolute pressure is the sum of gauge pressure and atmospheric pressure.
True or False:
Atmospheric pressure decreases with altitude.
True
Air density decreases at higher altitudes, reducing pressure.
Define:
Pascal’s principle
Pressure applied to a confined fluid is transmitted equally in all directions.
This principle is the basis for hydraulic systems.
What is the principle behind hydraulic brakes?
Pascal’s Principle
The principle states that pressure applied to a confined fluid is transmitted equally in all directions.This allows small forces, such as those present in brakes, to be amplified to stop a car.
Fill in the blank:
A fluid is considered ______ if its density is constant.
incompressible
Most liquids are nearly incompressible under normal conditions.
Define:
Surface tension
Cohesive force at the surface of a liquid allowing it to resist an external force.
## Footnote
It is responsible for phenomena like water droplets forming spherical shapes.
Why do non-Newtonian fluids behave differently than Newtonian fluids?
Their viscosity changes with applied force.
Examples include ketchup, cornstarch mixtures, and toothpaste.
True or False:
A fluid with higher density will exert more pressure at the same depth.
True
Pressure depends on both depth and fluid density.
Define:
specific gravity
Ratio of the density of a substance to the density of a reference substance, usually water for liquids and solids.
Specific gravity is dimensionless because it compares two densities without involving units. The reference substance is usually water for a liquid or solid, and air for a gas.
True or False:
A specific gravity greater than 1 means the object will float in water.
False
A specific gravity greater than 1 means the object will sink in water.
Floating occurs when specific gravity is less than 1, as the object is less dense than water.
What does Archimedes’ principle state?
A body submerged in a fluid experiences an upward buoyant force equal to the weight of the displaced fluid.
This explains why ships float and balloons rise in air.
Explain why oil floats on water.
Oil has a lower density than water.
Objects or substances with lower density than the fluid they are in will float.
Fill in the blank:
Hydrostatic pressure depends on fluid ______, gravitational acceleration, and depth.
density
This relationship is fundamental in understanding underwater pressures.
What factor influences whether an object sinks or floats due to buoyancy?
The object sinks when its weight exceeds the buoyant force.
A stone sinks because its density is greater than water’s.
Define:
Compressibility
Measure of how much a substance’s volume decreases under applied pressure.
Gases are highly compressible, while liquids are nearly incompressible.
Why is pressure independent of container shape?
Pressure is transmitted uniformly in all direction, so shape does not matter.
Pressure depends only on fluid height, density, and gravity, but not shape.
How does atmospheric pressure allow us to drink through a straw?
Removing air creates lower pressure inside the straw, and atmospheric pressure pushes the liquid up.
This principle is related to fluid statics and pressure gradients.
Define:
Ideal fluid
Fluid that cannot be compressed and has zero viscosity, meaning it flows without resistance.
Ideal fluids do not exist in reality but are a useful concept in fluid dynamics.
Fill in the blank:
The ideal gas law is written as ______.
PV=nRT
It relates pressure, volume, temperature, and the number of moles of gas.
True or False:
Boyle’s Law states that pressure and volume of a gas are inversely proportional at constant temperature.
True
For a gas, P₁V₁ = P₂V₂ when the temperature is constant.
Explain the relation between Boyle’s Law and scuba diving.
Boyle’s Law predicts how gas volume changes with pressure as divers descend or ascend.
Divers must adjust to avoid lung overexpansion or compression injuries.
Define:
Charles’s Law
Volume of a gas is directly proportional to its temperature at constant pressure.
As temperature increases, gas particles move faster, causing expansion. This is represented by the equation where V1/T1 = V2/T2, with V1 representing initial volume and V2 representing final volume.
How is Charles’s Law applied in hot air balloons?
Heating the air inside a hot air balloon increases its volume, making it less dense than the surrounding air, allowing the balloon to rise.
Define:
Gay-Lussac’s Law
Pressure of a gas is directly proportional to its temperature at constant volume.
Increasing temperature causes gas particles to collide more forcefully, raising pressure. In the equation P/T = k, P represents pressure of the gas, T is the absolute temperature of the gas, and k is a constant.
How does Gay-Lussac’s Law explain the risk of aerosol cans in high heat?
When an aerosol can is exposed to heat, the gas pressure inside increases due to the rise in temperature, potentially causing it to explode.
The relationship between pressure and temperature is crucial for understanding safety measures in pressurized containers.
Define:
Flow rate
Volume of fluid passing through a point per unit time.
Measured in units like m³/s or liters per second.
What is the standard unit for volumetric flow rate?
Cubic meter per second (m³/s).
This unit measures the volume of fluid passing through a cross-section per second.
Explain the relationship between flow rate and velocity.
Flow rate is directly proportional to velocity; a higher velocity leads to a greater flow rate if the cross-sectional area is constant.
Flow rate (Q) is calculated as Q=A⋅v, where A is the cross-sectional area and v is velocity.
Define:
Streamline flow
Fluid particles moving along smooth paths without turbulence.
Also called laminar flow, it occurs at lower velocities.
How does turbulence occur in fluid flow?
It occurs when a fluid moves at high velocities or around obstacles, causing chaotic, irregular flow patterns instead of smooth, laminar flow.
Turbulence is influenced by factors like velocity, fluid viscosity, and surface roughness, and it is characterized by swirling eddies and vortices.
Define:
Viscosity
Measure of a fluid’s resistance to flow.
Honey has high viscosity compared to water, which has low viscosity.
What are the standard units used to measure viscosity?
- Pascal-seconds (Pa·s) in the SI system
- Centipoise (cP) in the CGS system.
1 pascal-second (Pa·s) = 1000 centipoise (cP), and viscosity quantifies a fluid’s resistance to flow.
What does Bernoulli’s Principle state?
In a fluid flow, as the velocity of the fluid increases, the pressure within the fluid decreases.
This principle explains why airplanes achieve lift and how carburetors work.
What assumptions are made in Bernoulli’s principle?
- The fluid is ideal.
- The flow is steady and laminar.
- The fluid is incompressible.
- Viscosity effects are ignored.
Laminar flow means that each particle of the fluid follows a smooth path called streamline.
Fill in the blank:
In a Venturi tube, the _____-_________ area is narrowest where the velocity is highest.
Cross-sectional
This demonstrates the inverse relationship between velocity and pressure.
What physical quantities are combined in the Bernoulli equation?
It combines pressure, kinetic energy per unit volume, and potential energy per unit volume in a flowing fluid.
The equation is written as P+1/2ρv²+ρgh=constant.
Fill in the blank:
The Continuity Equation applies to fluids with constant ______.
density
This condition is typically assumed for incompressible fluids.
Fill in the blank:
The continuity equation describes the _______ ___ ______ in a steady fluid flow.
conservation of mass
The Continuity Equation states that the product of cross-sectional area and velocity is constant along a streamline.
What happens to the velocity of a fluid as the cross-sectional area decreases?
The velocity increases to maintain a constant flow rate.
This follows from the Continuity Equation, 𝐴1𝑣1=𝐴2𝑣2
Why is the Continuity Equation essential in pipe design?
It ensures that flow rates are maintained when pipe diameters change.
Engineers use this principle to avoid pressure drops and inefficiencies.
Why does a shower curtain move inward when the water is flowing?
The fast-moving water reduces air pressure inside the shower due to Bernoulli’s Principle.
This is a real-world example of the relationship between velocity and pressure.
True or False:
Faster-moving fluids exert higher lateral pressure.
False
Faster-moving fluids exert lower lateral pressure according to Bernoulli’s Principle.
How do airplane wings utilize Bernoulli’s principle?
The wing shape causes faster air above and slower air below, creating lift.
This pressure difference results in an upward net force on the wing.
How does Bernoulli’s equation explain the stability of a ball in a water jet?
Pressure differences due to varying velocities of water keep the ball in the stream.
Faster water movement on one side creates lower pressure, pushing the ball back into the stream.
What is the Magnus effect?
Phenomenon where a spinning object moving through a fluid creates a pressure difference, causing it to curve in its path.
This effect is commonly observed in sports like soccer, baseball, and tennis, where spin influences ball trajectory.
True or False:
The Magnus effect occurs because the spinning object alters the velocity of fluid around it, creating lift.
True
The Magnus effect arises from the interaction between the object’s spin and the surrounding fluid, causing asymmetric pressure distribution.
