Elastic Strain Energy

• What is elastic strain energy?

  Energy stored when a material is stretched

  
• What happens to work done before a material reaches its elastic limit?

  It is stored as elastic strain energy
• How is the work done represented in a force-extension graph?

  As the area under the graph

  
• Is the work done area under the graph valid for materials not obeying Hooke's law?

  Yes, it applies to all materials
• What shape represents the work done for materials obeying Hooke's law?

  A right-angled triangle
• How do you calculate the area under the graph for materials not obeying Hooke's law?

  Split into segments and sum areas
• What is the equation for elastic strain energy when Hooke's law is obeyed?

  E = $\frac{1}{2}F\Delta L$
• What does the variable E represent in the elastic strain energy equation?

  Elastic strain energy in joules
• What does the variable F represent in the elastic strain energy equation?

  Average force in newtons
• What does the variable $\Delta L$ represent in the elastic strain energy equation?


  Extension in meters
• How can elastic strain energy also be expressed using the spring constant?

  E = $\frac{1}{2}k(\Delta L)^2$
• What is breaking stress?

  Maximum stress before material fractures
• What does a material with high breaking stress indicate?

  It is ductile and can extend more
• What is ultimate tensile stress (UTS)?

  Maximum stress material can withstand
• What factors can affect UTS and breaking stress?

  Material condition, such as temperature
• Why is understanding breaking stress important for engineers?

  To select materials for structures under loads
• What is the breaking point on a stress-strain graph?

  Where the material fractures

  
• What happens to energy in a vertical spring system?

  • Energy converts between:
  • Elastic potential energy (EPE)
  • Kinetic energy (KE)
  • Gravitational potential energy (GPE)

  
• At position A in a vertical spring system, what is the state of energy?

  EPE is present, KE is 0, GPE is maximum

  
• At position B in a vertical spring system, what is the state of energy?

  EPE is present, KE is maximum, GPE is some

  
• At position C in a vertical spring system, what is the state of energy?

  EPE is maximum, KE is 0, GPE is minimum

  
• What energy types are considered in a horizontal mass on a spring system?

  • Only kinetic energy (KE)
  • Elastic potential energy (EPE)

  
• What should students remember about energy types in a spring system?

  Positions of maximum and zero energy types