4. Materials Flashcards
Define density.
The mass per unit volume of an object
What are the two possible units for density?
g/cm^3 OR kg/cm^3
State Archimedes’ Principle.
An object submerged in a fluid at rest has an upward buoynacy force (upthrust) equal to the weight of the fluid displaced by the object
What conditions are required for an object to float?
The weight of the object has to be equal to or less than the upthrust acting on it. Therefore the weight of the fluid displaced has to be greater than or equal to the objects weight.
What is the equation for viscous drag?
F = 6πηrv where F is viscous drag, η is the coefficient of viscosity of the fluid, r is the radius of the object and v is the velocity of the object.
Define viscous drag?
The frictional force between an object and a fluid which opposes the motion between the object and the fluid.
What are the conditions for Stoke’s Law?
Flow is laminar, object is small, object is spherical, motion between the sphere and the fluid is at a slow speed.
Define laminar flow.
Type of fluid in which the particles follow smooth paths in layers with each layer moving smoothly past the adjacent layers.
How can you change the viscosity of a fluid?
Viscosity is temperature-dependent and if you heat a fluid, its viscosity will decrease and vice versa.
State Hooke’s Law.
The extension of the material is directly proportional to the applied force (load) up to the limit of proportionality.
What is the equation used to represent Hooke’s law?
ΔF = kΔx where F is the applied force, k is the spring constant and Δx is the extension
How can you tell if a material obeys Hooke’s law by using a force extension graph?
There should be a straight line through the origin
Define the limit of proportionality.
The point beyond which Hooke’s law is no longer true when stretching a material (i.e. extension is no longer proportional to the applied force)
How can you identify the limit of proportionality on a force extension graph?
The point where the line on the graph beings to curve/no longer straight line through origin/begins to flatten out.
Define the elastic limit.
The maximum amount a material can be stretched and still return to its original length.
