Materials

• Forces that produce extension are known as tensile forces

  Forces that compress an object are known as compressive forces
• Force (f) = spring constant (k) x extension (x)
• Hookes law states that the extention is proportional to the force applied provided the limit of proportionality is not exceeded
• springs in parallel - Kt = K1 + K2 ..

  springs in series - 1/Kt = 1/K1 + 1/K2 ..
• Elastic deformation is a reversible change in the shape of an object due to tensile/compressive forces eg a spring
• Plastic deformation is an irreversible change in the shape of an object due to tensile/compressive forces eg a plastic bag
• Rules of Hookes law

  • the extension is directly proportional to the force applied
  • when theres no force applied the extension is zero
• Force constant depends on the material, size and shape of an object but can also be the stress and strain of an object
• Stress is the force per unit cross sectional area of a material

  Strain is the fractional change in length of an object
• Young modulus is the stress per unit of strain measured in pascals (Pa)
• $sigma (\sigma )=$$force(F)/ area(A )$
• $strain(\epsilon) =$$extension(x) / length(L)$
• $energy(E) =$$stress(\sigma)/ strain(\epsilon)$
• Elastic potential (E) = 0.5 x force (f) x extension (X)

  Elastic potential (E) = 0.5 x force constant (K) x extension squared (X^2)
• Stress strain graphs

  • limit of proportionality is the point where the stress is no longer linear to strain
  • Elastic limit is the point where it goes from elastic deformation to plastic deformation
  • Yield points are where there is a sudden extention with little increase in force
  • Breaking point is the point where the material breaks
  • Young modulus is the gradient of the linear part of the graph