Materials

• The gradient of a Force - Extension graph is the spring constant (k)
• The spring constant is the stiffness
• The unit of the spring constant is N/m
• What is Hooke's Law?

  Force ∝ Extension and F = K x X
• The spring constant of two springs placed in series vertically halves.

  
• The spring constant of two springs places in series next to each other is doubled.

  
• What is the equation to find the maximum force that can be applied to a spring to have linear deformation?

  P x A = F where P = Ultimate tensile strength
• Equation for Stress?

  Force (Tension)/Area (Cross sectional)
• Greek Letter for Stress?

  Sigma (σ)
• Unit of stress?

  Pascals (Pa)
• How many Pascals is 1 MPa?

  1000000 Pa
• Stress is a pushing tension force on an object and Strain is a pulling tension force on an object
• Strain is a proportional increase in length
• What is the Greek letter for Stain?

  Epsilon (ε)
• What's the equation for Stain?

  Strain = extension/Original length
• What is the unit of Strain?

  None: It's a ratio
• The gradient of a stress/strain graph is the Young Modulus
• Young Modulus = FL/AX
• The young modulus is a property of every material.
• How many Pascals is 1 GPa?

  1 Billion Pa
• Young Modulus = σ/ε
• The area under a force/extension graph is the work done to achieve the extension
• A part of the area under a force/extension graph is the work done to achieve that bit of extension.

  
• The work done to achieve an extension in a thing = the energy stored in the thing (EPE)
• If we stretch something, it stores elastic potential energy (EPE). If we compress it, it loses EPE.
• EPE = $\frac{1}{2} kx^2$
• Energy in a stretched thing = work done to stretch that thing = Area under force/extension graph
• efficiency = useful energy output/total energy input