Topic 4 Flashcards
What is the density of a material?
The density of a material is its mass per unit volume
State the equation used to calculate density
Density = Mass / Volume
What is the unit of density?
kg/m^3
When an object is submerged in a fluid, what determines the upthrust experienced?
The upthrust of a submerged object is equal to the weight of the fluid that 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?
The upthrust of the object will be equal to the weight of the liquid displaced.
Therefore, the maximum upthrust will be equal to the denstiy of the fluid x volume of object x gravitational field stength
The weight of the object is equal to the density of the object x volume of object x gravitational field strength
If the object’s density is greater, the weight will always be greater than the upthrust and the object will sink
What shaped objects does Stokes’ Law apply to?
Stokes’s law only applies to small spherical objects
What type of flow is required for Stokes’ Law to apply?
Laminar Flow
What does Stokes’ 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’ Law equation
F=6πηrv
η is the viscosity of the fluid
r is the radius of the sphere
v is the 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 no longer returns to its original shape once the deforming forces are removed. It will have permanent deformation
Express Hooke’s Law in words
The extension of an elastic object is directly proportional to the force that is applied to it, up to its limit of proportionality
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 elastic limit?
The point beyond which the object will no longer elastically deform, and will instead deform plastically
State the defining equation of Hooke’s Law
F=kΔx Force applied (N) = Stiffness constant x extension (m)
What is mechanical stress?
The force experienced by an object per unit area
State the equation for stress
σ = F/A Stress = Force / Area
What is the unit of stress?
N/m^2 or Pascals
State the equation for strain
ε = ΔL/L Strain = extension / original length
What is the unit of strain?
Strain is a unitless quantity because it is the ratio of two lengths
What does the Young Modulus of a material tell you?
A material’s Young Modulus is a measure of how much force is required for a given extension, regardless of the object’s dimensions
What equation is used to calculate a material’s Young Modulus?
Young Modulus = Stress / Strain
What unit is used for a material’s Young Modulus?
N/m^2
What is breaking stress?
Breaking stress is the maximum stress that an object can withstand before fracturing
What is the yield point?
The point beyond which the object will experience a large extension without substantial increase in the force applied
What type of energy is stored in an object that has been stretched?
Elastic Potential Energy
State two equations used to calculate the energy stored in a spring
E = 1/2 FΔx E = 1/2 KΔx^2
What does the gradient and area represent on a force-extension graph?
The gradient of the linear region represents the elastic constant (k)
The area is equal to the elastic potential energy stored in the spring
