Fluids and Solids Flashcards Preview

Fisica para el MCAT > Fluids and Solids > Flashcards

Flashcards in Fluids and Solids Deck (17):


Density: ρ=m/V


Archimedes' principle

buoyant force on an object = weight of the fluid displaced by the object.



FB = weightdisplaced = mdisplacedg =ρfluidVsubmergedg


When do objects float, sink, and rise upward in a fluid?

  • Things float when FB = Weight. 

  • Things will rise upward when FB > Weight. 

  • Things will sink when FB < Weight.


Pascal's Law

if you apply pressure on a liquid, the pressure is transmitted equally to all parts of the liquid.



Pressure in relation to depth

  • P=ρgh 

  • P is pressure, ρ is the density of the fluid; g is the gravitational constant, h is the height from the surface, or depth that the object is submerged.


Viscosity: Poiseuille flow

When a viscous fluid flows through a pipe, the flow has a front that is shaped like a parabola bulging outward.


Continuity equation 

A·v = constant, where v is linear flow rate (velocity).


Concept of turbulence at high velocities

  • Low velocity -> laminar flow. 

  • High velocity -> turbulent flow, forms eddies.


Surface tension

  • Surface tension gives the surface of a liquid the ability to support things that are very light. 

  • For example, insects can walk on water due to surface tension. 

  • Surface tension is due to the attraction between the molecules of the solvent.


Bernoulli's equation

P + ½ρv2 + ρgh = constant


Elastic properties (elementary properties) of solids

  • Stress: the pressure exerted on an object. σ = stress = F/A. 

  • Strain: the deformation of the object in the direction of the applied force divided by the original length. ε = strain = ΔL/L0.


Young's Modulus

  • Young's modulus = stress / strain. 

  • Young's modulus, the ratio between stress and strain, is constant until you reach the elastic limit, where things get permanently deformed.


Elastic Limit

The maximum stress something can handle before it breaks or become permanently deformed.


Thermal expansion coefficient

Things expand when temperature rises, and contract when temperature falls. 

ΔL = αL0ΔT 

ΔL is the change in length, L0 is the initial length, ΔT is the change in temperature, and α is the coefficient of linear expansion.


Expansion for area and volume

ΔV = βV0ΔT = 3αV0ΔT 

ΔA = γA0ΔT = 2αA0ΔT



  • Shear = stress / shear ratio.
  • Shear ratio = ΔL/L0.
  • When ΔL is very small compared to L0, Shear ratio is approximately the same as the shear angle.
  • Shear angle = tan-1ΔL/L.  Note: ΔL and L are perpendicular to each other.