The Physics of Fluids (Fluid Mechanics)

50 QUESTION_AND_ANSWER flashcards covering key concepts from the physics of fluids (fluid mechanics) based on the provided lecture notes.

What is the branch of physics that studies the behavior of fluids and the forces on them?

Fluid mechanics (the physics of fluids).

Define a fluid.

A substance that can flow; includes liquids and gases; cannot resist shear stress without moving.

Do fluids have a fixed shape?

No; they take the shape of their container; liquids form a free surface; gases fill the available volume.

Why can fluids flow easily?

Because of the loose arrangement of their particles; flow occurs when a shear stress is applied.

Can fluids resist shear stress like solids?

No; they continuously deform under any amount of shear force.

Compare compressibility between liquids and gases.

Liquids are almost incompressible; gases are highly compressible.

What does viscosity measure?

Resistance to flow (internal friction) of a fluid.

Define density.

Mass per unit volume; changes with temperature and pressure, especially in gases.

State Pascal's Principle.

In a confined fluid, any pressure applied is transmitted equally in all directions.

What is surface tension?

The cohesive force at the surface of a liquid that makes it behave like a stretched elastic sheet.

List key properties of fluids.

Density, pressure, viscosity; temperature affects density and viscosity; compressibility: gases compressible, liquids incompressible.

What is hydrostatics?

The study of fluids at rest.

What is Archimedes’ Principle?

A submerged body experiences an upward buoyant force equal to the weight of the displaced fluid.

Describe laminar flow.

Smooth, orderly flow.

Describe turbulent flow.

Chaotic flow with vortices.

Difference between steady and unsteady flow.

Steady: properties do not change with time; unsteady: properties vary with time.

Differentiate compressible and incompressible flow.

Gases are compressible; liquids are often treated as incompressible.

Define Newtonian and Non-Newtonian fluids.

Newtonian: constant viscosity; Non-Newtonian: viscosity varies with shear rate.

Give examples of Newtonian and Non-Newtonian fluids.

Newtonian: water; Non-Newtonian: ketchup, blood.

In transportation, which systems rely on incompressible fluid pressure?

Hydraulic brakes and steering.

Which principle explains lift in airplanes due to fluid flow?

Bernoulli’s principle (faster flow → lower pressure, contributing to lift).

What is a basic domestic use of fluids in water distribution?

Pressurized liquid distribution for water supply.

Name cooking processes that involve fluids.

Boiling, steaming, and frying; involve heat transfer with fluids.

What are IV drips?

Delivery of fluids and medications directly into the bloodstream.

What is blood flow?

The movement of blood, a fluid, through the circulatory system.

What is a ventilator?

A device that helps control breathing by regulating air flow.

What are pneumatics?

Use of compressed gases to power tools and machinery.

What are hydraulics?

Use of liquids for lifting and powering machinery.

How are fluids used in cooling systems?

Water or refrigerants remove heat from machines.

Name environmental phenomena related to fluids.

Weather movements (rain, wind), breathing (air flow), water cycle (evaporation, condensation, precipitation).

How are fluids involved in breathing and respiration?

Air (gas) moves in and out of the lungs as part of respiration.

How are refrigerants used in everyday appliances?

Transfer heat in air conditioners and refrigerators.

How are fluids used in showers and faucets?

Controlled flow of water.

What is capillary action?

Rise of liquid in narrow tubes due to cohesive and adhesive forces, driven by surface tension.

What happens to pressure with depth?

Pressure increases with depth.

What happens to velocity in a narrow pipe?

Velocity increases to conserve mass flow rate.

Why do fluids exert pressure equally in all directions?

Because molecular collisions are isotropic, transmitting pressure equally.

True or False: Fluids can resist shear stress without flowing.

False.

True or False: Pressure increases with depth.

True.

True or False: Air is considered a fluid.

True.

True or False: Surface tension arises from cohesive forces at the surface.

True.

True or False: The density of a fluid is defined as its mass per unit volume.

True.

True or False: Fluid flow rate remains constant if the cross-sectional area of the pipe changes.

True (in incompressible flow).

True or False: The viscosity of gases decreases with increasing temperature.

False (viscosity of gases typically increases with temperature).

True or False: Surface tension effects are more significant in larger bodies of liquid.

False (more significant in smaller bodies due to higher surface-area-to-volume ratio).

True or False: Increasing the temperature of a liquid will always decrease its viscosity and thereby increase its flow rate under the same applied force.

True (for most liquids; viscosity generally decreases with temperature).

True or False: A freshwater environment allows a floating object to float higher than in seawater.

True (freshwater is less dense than seawater).

What is the Bernoulli constant along a streamline?

P + 1/2 ρ v^2 + ρ g h remains constant.

What factors determine buoyancy besides gravity?

Density of the displaced fluid and the weight of displaced fluid (buoyant force).

What determines capillary rise height in a tube?

Capillary rise height depends on surface tension, contact angle, tube radius, fluid density, and gravity.