Fluids - Kaplan Physics Chapter 4 Flashcards
What are the two main characteristics that can differentiate between a fluid from a solid.
- Lack of resistance to deformation (Changes formation easily).
- Ability to take the container’s shape.
- A fluid will take the shape of its container, whereas solids have a definite shape.
- When a force is applied to a fluid, it will flow/be fluid/change form. Alternatively, solids are very resistant to deformation.
Define Density and identify its equation.
Density tells you how much mass is packed per volume.
p = m/v
- Colloquially, density is the amount of “compactness”.
- THINK: Metal Ball vs Wooden ball which are the same size. Metal ball is more dense due to it having a larger mass per volume.
Define Pressure and identify its equation.
Pressure is amount of force exerted over an area.
P = F/A
- Essentially measures the amount of molecules colliding with the walls of a container. More collisions = Higher Pressure.
*Think: It’s how knife cuts. A thin blade is pressed on a small area with great force.
Define Pascals Principle and identify its formula.
Pascals principle is the idea that when there is a contained fluid, and pressure is exerted on the container, the pressure change will be equally distributed to all the fluid.
P1 = P2 OR
F1/A1 = F2/A2
where P is pressure, F is force, and A is area. Measures Pressure at two points.
*Think: Squeezing a Toothpaste Tube
Define Archimedes’ Principle and identify its equation.
Archimedes’ Principle describes how when an object is placed in a fluid, the fluid will extert an upward force on the object. This is responsible for buoyancy.
Fb = p(fluid) * V(displaced) * g(gravity)
*For ex. If I throw a 3lb rock into lake, the lake V will be diplaced by 3lbs.
Identify the Arhcemides Equation and state how it can be used.
Fb = p(fluid) * V(displaced) * g(gravity)
Can be used to determine if something is sinking floating.
When Weight of object = Fb, then item is floating.
When Weight of object > Fb, then sinking.
Define Cohesion
Cohesion describes the ability/attraction of a substance for sticking to the same substance.
This creates surface tension.
Ex. Formation of water droplet
*Think: CO means together. Same molecules stick together.
Define Surface Tension
Property created by cohesion. Happens at the surface of a liquid and will minimize surface area.
Define Adhesion
Adhesion describes the ability/attraction of a substance for sticking to a different substance.
This creates capillary action.
Ex. Spilled water spreading on countertop.
*Think: ADD means more. Molecules stick to other molecules.
Define Capillary Action
Property as a result of adhesion.
Define Viscosity. Indicate what it means to have high vs low viscosity.
Viscosity descibes how freely a fluid will flow.
High viscosity = flows slowly
Low viscosity = flows freely
*Colloquially, this describes how “thick” a substance is.
Define Laminar/Turbulent Flow
Laminar Flow - Smooth flow of fluid in the same direction w/o mixing.
Turbulent Flow - Chaotic Flow.
Define Steamlines
The path that a fluid will take. Flow much be constant and not cross each other.
*Think: Considers the “line of the stream”
What is viscous drag?
Viscous drag describes a resistance that happens when an object is placed in a fluid and this fluid has different speeds through its layers.
*I like to think that fluid has an “inner conflict”
How to mathematically determine if laminar flow or turbulent flow is likely?
You must find Reynold’s Number by using the eq:
Re = (pvD)/(n)
where Re is Reynold’s number, p is density, v is velocity/flow speed, D is diameter of pipe, and n is viscosity.
Re < 2000 ; laminar
Re > 3000 ; turbulent
What is Bernouli’s Equation and why is it important?
Bernouli’s Eq:
constant = P + [(1/2)dv^2)] + pgh
*Also establishes that faster fluid = lower pressure (inverse relationship). [Different from the ideal gas law! This is due to energy of conservation of the moving fluid.]
*Think: Faster fluid, more kinetic energy dispersion, less energy available for pressure, hence lower pressure.
Which Eq. Would you use to determine rate of flow for laminar pipe?
Use Poiseulle’s Law/Equation.
Q = (π * r^2 * ∆P)/(8 * n * L)
where Q is rate of flow, ∆P pressure difference, n is viscosity , and L is length of pipe.
How do fluid dynamics apply to the circulatory system?
- Application to streamlines
- Application to pressure gradient
- Application to Bernouli’s
- Application to Viscosity
- When the line of stream is close together, the flow will be faster. This is true for narrow vessels, like capillaries.
- The pressure gradient is how blood moves throughout the heart.
- Arteries, expand and contract to maintain blood flow during diastole.
- Blood is more viscous than water so it impacts flow. Increased viscosity (ex. due to hydration) increases resistance and blood pressure.
How do fluid dynamics apply to the respiratory system?
- Application to pressure gradient
- Application to surface tension
- ## Application to Venturi’s Effect
- Air moves in and out of the lungs because of pressure gradient.
- Viola in lungs are lined with liquid, but create surface tension. Surfactant will reduce tension so that Abiola does not collapse.
- Narrow airways (ex. asthma) can lead to faster airflow, which can lower pressure.
