MCAT Physics: Thermodynamics and Fluids

heat

transfer of non-mechanical energy between a system and its environment, an extensive property

extensive property

a property that depends on the amount of matter (mass) in a sample

temperature

macroscopic measure of the average internal (thermal) energy of a system, an intensive property

intensive property

a property that depends on the type of matter in a sample, not the amount of matter

the thermal energy of an object is proportional to

the mass and the temperature

when two substances are in contact, heat transfers between them until they achieve

thermal equilibrium (the same temperature)

conduction

heat transfer through solids in contact

convection

heat transfer through fluid circulation

radiation

P=kA (delta T/L)

heat transfer by emission/absorption of electromagnetic energy

First Law of Thermodynamics

E = Q -W where W = work done by the system

the internal energy of a closed system depends upon how much heat energy is transferred into the system and how much work the system does on its surroundings

average kinetic energy of molecules

1/2mv^2 = 3/2KbT

ideal gas law

PV=nRT

If an ideal gas transitions from one state to another

The change in energy is the same no matter how you get from state 1 to state 2

pressure

P = F/A

distribution of a perpendicular force over an area

Isobaric process

Energy = Q-P(delta)V

constant pressure, an ideal gas in a metal cylinder with a frictionless piston pushed down to maintain equilibrium

isochoric processes

Energy = Q

constant volume, an ideal gas in a metal cylinder with the piston locked in place

isothermal processes

Q=W

constant temperature, an ideal gas in a metal cylinder with a frictionless piston is submerged in a large water bath that maintains a constant temperature

adiabatic processes

Energy = -W

no heat transfer, an ideal gas in a metal cylinder with a frictionless piston that is insulated

PV diagrams

work is the area under the curve of this graph

second law of thermodynamics

entropy of an isoalted system either stays the same or increases during any thermodynamic process

entropy

the measure of the disorder of a system

isolated system

A system that can exchange neither energy nor matter with its surroundings.

closed system

a system in which only energy can be exchanged

open system

A system in which matter and energy can enter from or escape to the surroundings.

fluid

material that flows/takes the shape of its container when at rest. Ex: liquid and gases

density

rho=mass/volume

specific gravity

gs=density/density of water

weight of a fluid

W= mg = ρVg

hydrostatic gauge pressure

Pgauge= rho(g)(D), where rho is the density of the fluid and D=depth to the bottom of the object

pressure due to being immersed in a fluid; gauge is 0 at the surface

total pressure of hydrostatic system

Ptot = Psurface + Pgauge

buoyant force

F = rhoVg; where rho is the density of the fluid, V is the volume submerged, and g is gravity

the upward force exerted on an object either partially or completely submerged in a fluid due to the pressure difference between the top and bottom of the object

flow rate

f=Av

the volume of a fluid moving through a particular cross-sectional area per unit of time, assuming flow speed is constant across the area

continuity

A1v1=A2V2

for an incompressible (constant density) fluid, the flow rate is constant throughout a pipe

ideal fluid flow

Incompressibility (density constant)

negligible viscosity (no intrafluidic friction)

laminar (streamline) flow (no turbulence, no eddies or crossing flow streams)

flow rate is steady (no fluid is added or subtracted).

violations to ideal flow

gas getting compressed/expanding

flow of viscous fluids

air turbulence in storms

laminar flow

The movement of water particles in straight-line paths that are parallel to the channel. The water particles move downstream without mixing.

turbulent flow

an irregular, mixing flow pattern

bernoulli's equation

P₁+ρv₁²/2+ρgy₁=P₂+ρv₂²/2+ρgy₂, where P=absolute pressure, ρ=density, and y=height relative to reference height

describes ideal fluid flow, consrvation of energy for fluids

special cases to Bernoulli's equation

-At any two points of equal heigh, faster fluid flow means lower pressure

-Any fluid exposed to the atmosphere is at atmospheric pressure