Materials Flashcards
(36 cards)
What is the density of a material?
The density of a material is its mass per unit volume
What is unit of density?
kgm^-3
When an object is submerged in a fluid, what determines the upthrust it experiences?
The upthrust of a submerged object is equal to the weight of the fluid it displaces
What determines whether an object floats or sinks?
The balance between the weight and upthrust of the object. If the weight exceeds the upthrust, the object will sink.
Why will a uniform object with a density greater than that of the liquid it is submerged in, always sink?
- upthrust of the object = weight of fluid displaced
- therefore, max upthrust = density of fluid * volume of object * g
- weight of object = density of object * volume of object * g
- if the object’s density is >, the weight is always > than upthrust
- object will sink
What shaped objects does Stokes’s Law apply to?
Stokes’s Law only applies to small spherical objects
What type of flow is required for Stokes’s Law to apply?
Laminar Flow
What does Stokes’s Law allow you to calculate?
The viscous drag force that a small spherical object experiences when falling at low speeds through a viscous fluid with laminar flow.
State the Stokes’s Law equation
F = 6 π η r v
η = viscosity of the fluid
r = radius of sphere
v = speed of the sphere
What is elastic deformation?
An object has undergone elastic deformation if it returns to its original shape once the deforming forces are removed
What is plastic deformation?
An object has undergone plastic deformation if it doesn’t return to its original shape once the deforming forces are removed. It will have permanent deformation
What is Hooke’s Law
The extension of an elastic onject is directly proportional to the force that is applied to it, up to its limit of proportionailty
What is the limit of proportionality?
The point beyond which the force and extension will no longer be directly proportional to each other - Hooke’s Law is no longer obeyed
What is the the elastic limit?
The point beyond which the object will no longer elastically deform and will instead deform plastically.
What is the order of points on the Force extension graph?
LopElYp
- limit of proportionality
- elastic limit
- yield point
What is the yield point?
The point beyond which the object will experience a large extension without substantial increase in the force applied
Equation for Hooke’s Law
F = k Δx
F = force applied (m)
k = stiffness constant
Δx = extension (m)
What is mechanical stress?
The force experienced by an object per unit area
equation for stress
Stress = force / cross-sectional area
unit for stress
Nm^-2
equation for strain
Strain = change in length / original length
unit of strain
none, it is a ratio
What does the Young Modulus of a material tell you?
It shows a measure of how much force is required for a given extension, regardless to the object’s dimensions
equation for Young Modulus
Young modulus = Stress/Strain
