6.1.1
Bulk Properties of Solids
Hooke's Law
Hooke's Law
Hooke's law is a proportional relationship between the force experienced and the extension observed. The relationship exists up to an elastic limit.


Hooke's law
Hooke's law
- Hooke's law is the relationship that the force F experienced by an extensible object is proportional to its extension ΔL:
- F α ΔL
- The constant of proportionality is labelled k and is called the stiffness constant.
- This gives the equation:
- F = kΔL
- The force acts to restore the object back to its original shape, so it acts in the opposite direction to that of the extension.


Limit of proportionality
Limit of proportionality
- Hooke's law is a relationship between two quantities. But, this relationship does not always hold.
- When a force-extension graph is linear, Hooke's law applies.
- When a force-extension graph is non-linear, Hooke's law does NOT apply.


Elastic limit
Elastic limit
- An object (e.g. a spring) is elastic if it returns back to zero extension when the load on it is removed.
- The elastic limit is the maximum force the spring can sustain and then return to zero extension.
 - Force extension graph and limit of proportionality (1)-min,h_400,q_80,w_640.png)
 - Force extension graph and limit of proportionality (1)-min,h_400,q_80,w_640.png)
Gradient of force-extension graphs
Gradient of force-extension graphs
- The gradient of a force-extension graph is the value of the constant of proportionality, k.
- For springs, this is the familiar spring constant.
Strain and Stress
Strain and Stress
Summary values of materials are useful for engineers to compare the qualities of different materials. Two examples of summary values are stress and strain.


Effect of forces
Effect of forces
- Forces can change an object's shape.
- The study of stress and strain is a study of how forces change an object's shape.
- Some forces stretch the object.
- These forces are called tensile forces.
- Some forces squash the object.
- These forces are called compressive forces.
- Some forces stretch the object.


Stress
Stress
- Stress can be defined as:
- Stress =
- If the force is tensile, then the stress is positive.
- If the force is compressive, then the stress is negative.
- The units are newtons per metre squared (N/m2) or pascals (Pa).


Strain
Strain
- Strain can be defined as:
- If the force is tensile, then the strain is positive.
- If the force is compressive, then the strain is negative.
- There are no units for strain because strain is a ratio.


Elastic strain energy
Elastic strain energy
- When an elastic object is stretched, energy needs to be supplied to the object to stretch the object.
- The supplied energy is the elastic strain energy.
- The elastic strain energy can be determined from the area underneath a force-extension graph.


Breaking stress
Breaking stress
- Breaking stress is the stress required to break the material.
- The maximum tensile stress an object can withstand is called the ultimate tensile stress.
- Some materials can undergo some strain beyond the point of ultimate tensile stress before breaking.
Plastic and Brittle Behaviour
Plastic and Brittle Behaviour
Objects respond differently to a wide range of stresses and strains.


Plastic behaviour
Plastic behaviour
- An object deforms plastically if it undergoes permanent deformation under stress.
- Plastic behaviour occurs after the elastic limit.
- Stretching strawberry laces is an example of plastic behaviour.
- To identify areas of plastic behaviour on a force-extension graph, look to the right of the elastic limit point.


Brittle behaviour
Brittle behaviour
- An object is brittle if it breaks suddenly and cracks. There will be very little plastic behaviour shown.
- An example of a brittle food is hard sugar sweets.


Fractures
Fractures
- Fractures happen when the material completely breaks.
1Physical Quantities & Units
2Measurement Techniques
3Kinematics
4Dynamics
4.1Momentum & Newton's Laws of Motion
4.2Non-Uniform Motion
4.3Linear Momentum & Conservation
4.4Force, Density & Pressure
4.4.1Fields
4.4.2Force in Uniform Fields
4.4.3Friction
4.4.4Buoyancy
4.4.5Terminal Speed
4.4.6End of Topic Test - Acceleration Due to Gravity
4.4.7Centre of Mass
4.4.8Forces & Equilibrium
4.4.9End of Topic Test - Scalars & Vectors
4.4.10Moments
4.4.11End of Topic Test - Moments & Centre of Mass
4.4.12Density
4.4.13Pressure
4.5Work, Energy & Power
5Gravitational Fields
5.1Gravitational Fields (A2 only)
6Deformation of Solids
7Thermal Physics
7.1Thermal Physics
7.1.1Temperature
7.1.2Measuring Temperature
7.1.3Ideal Gas Law
7.1.4Ideal Gases
7.1.5Boyle's Law & Charles' Law
7.1.6Molecular Kinetic Theory Model
7.1.7Molecular Kinetic Theory Model 2
7.1.8Thermal Energy Transfer
7.1.9Thermal Energy Transfer Experiments
7.1.10End of Topic Test - Thermal Energy & Ideal Gases
7.1.11First Law of Thermodynamics
8Oscillations
8.1Simple Harmonic Motion
8.2Waves
8.2.1Progressive Waves
8.2.2Intensity of Waves
8.2.3Wave Speed & Phase Difference
8.2.4Longitudinal & Transverse Waves
8.2.5End of Topic Test - Progressive Waves
8.2.6Electromagnetic Waves
8.2.7Doppler Effect
8.2.8Sound Waves
8.2.9Measuring Sound Waves
8.2.10End of Topic Test - Waves
8.2.11Ultrasound Imaging
8.2.12Ultrasound Imaging 2
9Communication
9.1Communication Channels
9.2Digital Communication
10Electric Fields
10.1Electric Fields
11Current Electricity
11.1Current Electricity
11.1.1Basics of Electricity
11.1.2Mean Drift Velocity
11.1.3Current-Voltage Characteristics
11.1.4End of Topic Test - Basics of Electricity
11.1.5Resistivity
11.1.6End of Topic Test - Resistivity & Superconductors
11.1.7Power and Conservation
11.1.8Microphones
11.1.9Components
11.1.10Relays
11.1.11Strain Gauges
12Magnetic Fields
12.1Magnetic Fields
13Modern Physics
13.1Quantum Physics
13.1.1The Photoelectric Effect
13.1.2The Photoelectric Effect Explanation
13.1.3End of Topic Test - The Photoelectric Effect
13.1.4Collisions of Electrons with Atoms
13.1.5Energy Levels & Photon Emission
13.1.6Wave-Particle Duality
13.1.7End of Topic Test - Absorption & Emission
13.1.8Band Theory
13.1.9Diagnostic X-Rays
13.1.10X-Ray Image Processing
13.1.11Absorption of X-Rays
13.1.12CT Scanners
13.2Nuclear Physics
13.2.1Rutherford Scattering
13.2.2Atomic Model
13.2.3Isotopes
13.2.4Stable & Unstable Nuclei
13.2.5A-A* (AO3/4) - Stable & Unstable Nuclei
13.2.6Alpha & Beta Radiation
13.2.7Gamma Radiation
13.2.8Particles, Antiparticles & Photons
13.2.9Quarks & Antiquarks
13.2.10Particle Interactions
13.2.11Radioactive Decay
13.2.12Half Life
13.2.13End of Topic Test - Radioactivity
13.2.14Nuclear Instability
13.2.15Mass & Energy
13.2.16Binding Energy
13.2.17A-A* (AO3/4) - Nuclear Fusion
Jump to other topics
1Physical Quantities & Units
2Measurement Techniques
3Kinematics
4Dynamics
4.1Momentum & Newton's Laws of Motion
4.2Non-Uniform Motion
4.3Linear Momentum & Conservation
4.4Force, Density & Pressure
4.4.1Fields
4.4.2Force in Uniform Fields
4.4.3Friction
4.4.4Buoyancy
4.4.5Terminal Speed
4.4.6End of Topic Test - Acceleration Due to Gravity
4.4.7Centre of Mass
4.4.8Forces & Equilibrium
4.4.9End of Topic Test - Scalars & Vectors
4.4.10Moments
4.4.11End of Topic Test - Moments & Centre of Mass
4.4.12Density
4.4.13Pressure
4.5Work, Energy & Power
5Gravitational Fields
5.1Gravitational Fields (A2 only)
6Deformation of Solids
7Thermal Physics
7.1Thermal Physics
7.1.1Temperature
7.1.2Measuring Temperature
7.1.3Ideal Gas Law
7.1.4Ideal Gases
7.1.5Boyle's Law & Charles' Law
7.1.6Molecular Kinetic Theory Model
7.1.7Molecular Kinetic Theory Model 2
7.1.8Thermal Energy Transfer
7.1.9Thermal Energy Transfer Experiments
7.1.10End of Topic Test - Thermal Energy & Ideal Gases
7.1.11First Law of Thermodynamics
8Oscillations
8.1Simple Harmonic Motion
8.2Waves
8.2.1Progressive Waves
8.2.2Intensity of Waves
8.2.3Wave Speed & Phase Difference
8.2.4Longitudinal & Transverse Waves
8.2.5End of Topic Test - Progressive Waves
8.2.6Electromagnetic Waves
8.2.7Doppler Effect
8.2.8Sound Waves
8.2.9Measuring Sound Waves
8.2.10End of Topic Test - Waves
8.2.11Ultrasound Imaging
8.2.12Ultrasound Imaging 2
9Communication
9.1Communication Channels
9.2Digital Communication
10Electric Fields
10.1Electric Fields
11Current Electricity
11.1Current Electricity
11.1.1Basics of Electricity
11.1.2Mean Drift Velocity
11.1.3Current-Voltage Characteristics
11.1.4End of Topic Test - Basics of Electricity
11.1.5Resistivity
11.1.6End of Topic Test - Resistivity & Superconductors
11.1.7Power and Conservation
11.1.8Microphones
11.1.9Components
11.1.10Relays
11.1.11Strain Gauges
12Magnetic Fields
12.1Magnetic Fields
13Modern Physics
13.1Quantum Physics
13.1.1The Photoelectric Effect
13.1.2The Photoelectric Effect Explanation
13.1.3End of Topic Test - The Photoelectric Effect
13.1.4Collisions of Electrons with Atoms
13.1.5Energy Levels & Photon Emission
13.1.6Wave-Particle Duality
13.1.7End of Topic Test - Absorption & Emission
13.1.8Band Theory
13.1.9Diagnostic X-Rays
13.1.10X-Ray Image Processing
13.1.11Absorption of X-Rays
13.1.12CT Scanners
13.2Nuclear Physics
13.2.1Rutherford Scattering
13.2.2Atomic Model
13.2.3Isotopes
13.2.4Stable & Unstable Nuclei
13.2.5A-A* (AO3/4) - Stable & Unstable Nuclei
13.2.6Alpha & Beta Radiation
13.2.7Gamma Radiation
13.2.8Particles, Antiparticles & Photons
13.2.9Quarks & Antiquarks
13.2.10Particle Interactions
13.2.11Radioactive Decay
13.2.12Half Life
13.2.13End of Topic Test - Radioactivity
13.2.14Nuclear Instability
13.2.15Mass & Energy
13.2.16Binding Energy
13.2.17A-A* (AO3/4) - Nuclear Fusion
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