Materials

Density

Density

Mass per unit volume

Upthrust

Upwards force on objects in fluids

Archimedes' principle

The upthrust experienced by an object is equal to the weight of the fluid it displaces

Upthrust equation

Upthrust = ρVg where ρ is the density of the fluid, V is the volume of the object, and g is gravity

Stokes' law

The viscous drag force experienced by a small, spherical object moving slowly with laminar flow

Stokes' law equation

F = 6πrηv where r is the radius of the sphere, η is the viscosity of the liquid, and v is the terminal velocity

Laminar flow

Particles in a fluid move at low velocities parallel to each other and don't interact

Turbulent flow

Particles in a fluid move at high velocities and mix between layers in erratic directions

Viscosity

Measure of how resistant a fluid is to deformation

What is viscosity dependent on?

Temperature. Increase causes a decrease in viscosity in liquids and an increase in viscosity in gases

Hooke’s law

Extension is directly proportional to the force applied, given that the environmental conditions are kept constant

Hooke’s law equation

ΔF = kΔx where F is force, k is the stiffness and Δx is the extension

Young modulus

Value which describes the stiffness of a material

Stress

Force applied per unit cross-sectional area

Strain

Caused by stress, and is defined as the change in length over the original length

Young modulus equation

Young Modulus = Stress/Strain or E = σ/ε

Hooke’s law on a force-extension graph

Straight line through the origin

The limit of proportionality (P)

The point after which Hooke’s law is no longer obeyed

Elastic limit (E)

Just after the limit of proportionality. Beyond this, the material will deform plastically

Yield point

Point at which the material begins to stretch without an increase in load

Elastic deformation

Where a material returns to its original shape once the force applied is removed

Plastic deformation

Where a material’s shape is changed permanently

Stress-strain graphs

Similar to force-extension graphs, however they describe the behaviour of a material rather than the behaviour of a specific object

Ductile

Can undergo large amounts of plastic deformation before fracturing

Brittle

Where a material undergoes little to no plastic deformation before breaking

Plastic

Where a material will experience a large amount of extension as the load is increased

Elastic strain energy

When work is done on a material to stretch or compress it, this energy is stored as elastic strain energy