C2 Physics Flashcards
Define density
The density of a material is defined as the mass per unit volume of the material
Density (p) ( kg m -2) = mass (m) (kg) / volume (v) (m3)
Define elasticity
When a force is applied, it can be deformed but it can return back to its original shape
Define soft
Can be easily deformed, cut, bent or pressed
Define flexible
Can easily bend without breaaking
Define plastic deformation
Permanent change in shape or size after stress exceeds the yield strength. It does not return to original shape.
Ductile
Material can be stretched into wires or cables or put under tension without breaking. It is deformed under tensile stress.
Brittle
Easily shatters after elastic limit, cant be permanently stretched. Strong under compression, weak under tension.
Malleable
When force is applied, can be hammered into shape or extended easily. Not all malleable materials are ductile
Strong
Takes a huge amount of force to break/deform.
Hard
Able to withstand a high amount of force without deformation or scratching.
Stress Strain Curve
Shows relationship between stress and strain by gradually adding weight and measuring deformation.
Elastic limit
Point on stress curve where plastic deformation occurs so will not return back to original shape.
Strength
Maximum stress the material can bear before material fails (fractures).
Yield point
Point where solid material that is being stretched, starts to change permanently.
Point on a stress - strain curve that indicates elastic limit and start of plastic deformation.
Creep
Solid material under stress permanently deforms over time, moving at a slow rate. More severe when heat is applied.
Fatigue
Progressive and structural damage leading to weakening of a material due to low levels of stress if theres repeated loading and unloading.
Elastic Hysterisis
The difference between the strain energy needed to generate a given stress in a material and the materials elastic energy at that stress.
E.g. Elastic bands - stretching elastic band transfers kinetic energy to the band. Energy is needed to stretch the bands molecules, which is then stored as thermal energy increasing the temperature.
Define Hookes Law
The extension produced by a force in a wire or spring, is directly proportional to the force applied, up to the limit of proportionality
Force (f) (N) = spring constant (k) (Nm-3) x extension (change in x) (m)
Define strain energy
The area under a force / extension graph for an elastic material represents work done in stretching the material
Work done ( W) = 1/2 x Force (F) x change in x
Equation to work out tensile stress
Stress (Pa) = force (N) / cross sectional area (m2)
Equation to work out tensile strain
Strain = extension (change in length) (m) / original length (m)
Define youngs modulus
How difficult it is to change shape of material. Measure of stiffness.
Ratio of stress to strain for a material (how material will behave when force is applied).
YM (Pa or Nm -2) = tensile stress (f/a) (Pa) / tensile strain (e/original l)
- Always convert to metres
- High numbers mean stronger
- equation for area of a circle = pie r squared
What does the straight line in the stress - strain curve represent?
Shows material is obeying hookes law (straight line thru origin)
What is the limit of proportonality?
Point where material stops obeying hookes law, point where the line starts to bend. It will return to its original shape if stress is removed.
What is the elastic limit?
Highest point of stress on a material where it will return back to its original shape.
What is yield strength?
The point where a material begins to deform permanently.
What is the difference between stress - strain graphs and force - extension graphs?
Stress - strain graphs show general bhv of a material.
Force - extension graphs are specific for tested objects and depends on dimensions.
Define ultimate tensile strength
Highest stress a material can sustain just before it fails.
What happens when a stress strain graph is showing a brittle material?
When the stress reaches a certain point, the material suddenly fractures and does not go thru plastic deformation. Straight line.
What makes a material malleable and ductile?
Atoms are arranged in regular layers and can roll over eachother without breaking bonds.
Why do materials like rubber produce heat during elastic hysterisis?
Repeatedly stretching and releasing rubber band will cause it to heat up due to hysterisis, this is because the rubber is transferring energy to its molecules, resulting in heating.
What happens when a graph is showing a ductile material?
Line will start bending as material is undergoing plastic deformation. Line will be up and down.
What happens when a graph is showing a strong material?
Line will be straight with a tiny bend at the end.
What happens when a graph is showing a plastic material?
Loading line will start bending almost straightaway, as plastic deformation is seriously occurring.
Then the unloading line will go diagonally straight down
What type of material has a large force before fracture?
Strong material.
What type of material has a small plastic region?
Brittle material.
What type of material has a large plastic region?
Ductile material.
What type of material has a steep gradient before limit of proportionality?
Stiff material.
What happens when a graph is showing an inelastic material?
Loading line will stay straight until right at the end
Unloading line will go parallel underneath from where line curved off
