Materials

Materials

1. Hookes Law

   • Extension is proportional to force
     • F=Kx
       • K= wire constant
     • Also applies to springs
       • It also happens in more than just metals
   • The law is true until a point
     • There's a limit to the force this works with
     • This point is know as the limit of proportionality
     • After the point of 'Elasticity' the material will be permanently deformed
   • Deformations
     • Plastic- The material is permanently stretched
     • Elastic- It'll return to its normal shape once the force is removed

2. Stress, Strain and Elastic strain energy

   • A force stretching a material is tensile
     • STRESS- σ (sigma)
       • σ= F/A
       • The unit is pascals
     • STRAIN- ε (epsilon)
       • ε= Δx/x
       • This has no unit
   • A force compressing a material is compressive
   • Elastic strain energy is the area under a force-extension graph
   • Calculating Energy in a stretched material
     • We use average force since it isn't constant
     • WORK DONE = 0.5 * F * Δx
     • Elastic Strain energy= 0.5 * F * Δx
     • SINCE HOOKES LAW APPLIES
     • ESE= 0.5 * K * Δx(2)

3. Young Modulus

   • YM is Stress / Strain
     • E= σ / ε
   • Stress and strain are proportional until the limit of the material is breached
   • The unit is Pascals (the same as stress)
   • It's the measure of the stiffness of a material

4. Density, Upthrust & Viscosity

   • DENSITY- is mass per volume
     • Its the measure of compactness
     • Density= Mass/Volume
       • Its unit is gcm(-3) OR kgm(-3)
   • Objects in fluid experience upthrust
     • Pressure is force applied per unit area
       • Pressure= force / area
         • Unit is pascals
     • Pressure depends on depth in liquid (h)
       • Density of the fluid (ρ)
         • And gravitiy (g)
         • Pressure= hρg
     • Upthrust = Weight of fluid displaced
   • Viscous drag acts on object in fluids moving
     • It's a form of friction
     • STOKES LAW
       • F=6πηrv
         • η- viscosity of the fluid
         • r- radius
         • v- speed
       • Viscosity can change with temp
       • It only applies for slow moving objects with laminar flow