Hooke's Law>>> ∆F = k∆x
where k is the stiffness of the object
Stress>>> σ=F/A
where F is force and A is cross sectional area
Strain>>>
... [Show More] ε=∆x/x
where x is the original length of the material and ∆x is the extension
Young Modulus>>> Stress/Strain
Tensile stress/strain>>> Causes the length of the material to increase, the forces act away from the center
Compressive stress/strain>>> Causes the length of the material to decrease, the forces act towards the center
Force Extension graph>>>
Stress strain graph>>>
Stress Strain Graphs for Different Materials>>> Stiffer materials have a steeper gradient.
Stronger materials have a large breaking stress
Brittle materials have a very small plastic regions
Stress Strain Graph for Rubber>>>
Limit of Proportionality>>> *The point until which force and extension (or stress and strain) are directly proportional. After this point it may behave elastically, but they will no longer be proportional*
Elastic Limit>>> *The point beyond which the material is permanently deformed, it won't return to it's original shape*
Yield Point>>> *Beyond this point the material suddenly undergoes a large increase in extension (it 'gives') as the atomic substructure is rearranged*
Breaking stress>>> *The value of stress in a material when it breaks*
Elastic Deformation>>> *Region where the material will return to its original shape when the stress is removed*
Plastic Deformation>>> *Permanent deformation caused by strain when stress exceeds a certain value. The material won't return to it's original shape.*
Elastic Strain Energy>>> ∆E(el) = F∆x
As this is the area under a force extension graph.
What does it mean for a material to be hard?>>> *It is resistant to indentation or scratching*
What does it mean for a material to be stiff?>>> *It has a large young modulus and so can withstand a large load with just a small extension*
What does it mean for a material to have a high tensile stress?>>> *It can withstand a large force under tension before breaking*
What does it mean for a material to be ductile?>>> *Can be drawn out into wires as it undergoes a lot of plastic deformation*
What does it mean for a material to be brittle?>>> *Shatters under a sudden force as it cracks with little or no plastic deformation just beyond the elastic limit due to the propagation of the cracks*
Density>>> Density = Mass/volume
Upthrust>>> Due to Archemides' principle, upthrust is equal to the the weight of the fluid displaced. This can be found if you know the density of the fluid and the volume of the object
Floating>>> If an object is floating, then the weight of the fluid displaced = the weight of the object
Hydrometer>>> A hydrometer is an instrument for measuring the density of liquids.
The inner (solid) part of the hydrometer has a constant mass and so in different liquids it will float to different extents
Laminar flow>>> -Layers are parallel to each other (don't mix)
-No abrupt changes in direction
-Fluid has a small velocity
Turbulent flow>>> -Layers mix
-Fluids move at a high velocity
-Abrupt changes in speed and direction
-Eddies
Viscosity>>> The resistance of a fluid to flowing
Viscosity: Fluids>>> As temperature increases, viscosity decreases (as intermolecular forces decrease)
Viscosity: Gas>>> As temperature increases, viscosity increases (as greater kinetic energy means more collisions between particles thus more friction)
Stokes Law>>> F = 6πηrv
Only works for
-Small cylindrical objects
-Travelling at small velocities
-Where there is laminar flow
Terminal velocity>>> Need to know how to explain this as well
Terminal velocity equation derivation>>> -Weight = upthrust + stokes law
-m(s)g = weight of fluid displaced + 6πηrv(t)
-W(s) = 4/3 x π r^3 p(f) g + 6πηrv(t)
4/3 x π r^3 p(s) g = 4/3 x π r^3 p(f) g + 6πηrv(t)
Rearranged to make V(t) the subject and simplified you get:
v(t) = (2r^2 x g (p(s)-p(f)))/9η
Wavelength>>> *The displacement between a point on a wave and the identical point on the next wave*
Period>>> *The time taken for one complete oscillation*
Frequency>>> *The number of complete oscillations in one second*
f = 1/T
v = fλ
Amplitude>>> *The maximum displacement from the mean position*
Phase>>> The position of a point on a wave at a specific moment in time
Transverse Waves>>> *Direction of oscillation is perpendicular to the direction of propagation of the wave*
Transverse waves are composed of particles that make up the wave oscilating up and down
Longitudinal Waves>>> *Direction of oscillation is parallel to the direction of propagation of the wave*
A longitudinal wave is composed of areas of compression (high pressure) and rarefaction (low pressure) caused by particles oscillating backwards and forwards
Wavefront>>> *A line joining points at the same position along a wave*
Coherance>>> *Waves which have are of the same frequency, wavelength, polarisation and in a constant phase relationship*
Path Difference>>> *the difference in distance from each source to a particular point*
If wave source is coherent can be used with the phase of the waves to see how the waves will interfere.
Path difference of a whole number of wavelengths gives complete constructive interference, path difference with an extra half a wavelength gives complete destructive interference
Superposition>>> *when two or more waves of the same type meet at a point the resultant displacement of will be the sum the individual displacements*
Interference>>> A special kind of superposition where the waves are coherant
Standing Wave>>> A standing wave is formed when a wave and it's reflection superpose to form areas of complete destructive interference (nodes) and complete constructive interference (anti nodes)
One standing wave was 2 ovals in it.
The fundamental frequency has oval in it
Equation for speed of a transverse wave on a string>>> V = √T/µ
Diffraction>>> *The change in direction of a wave when it passes through a gap of similar size to it's wavelength*
Diffraction patterns>>> There is a central maxima in the middle (where the light is the most intense) and then a pattern of minima (dark areas) and smaller maxima.
These patterns are created because light rays moving at different angles interfere with each other. Where this interference is destructive at the screen, you have a minima. Where it is constructive, there is a maxima. Double slit diffraction occurs the same way.
When this is done with coloured light, violet is to the central side of each maxima and red light on the other side [Show Less]