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Materials

Materials. Fluids and Fluid Flow 1 Fluids and Fluid Flow 2 Force and Extension Stress, Strain, and the Young Modulus. Turbulent + Laminar Flow. Laminar /Streamline Flow – layers do not cross each others paths. Occurs at lower speeds.

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Materials

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  1. Materials • Fluids and Fluid Flow 1 • Fluids and Fluid Flow 2 • Force and Extension • Stress, Strain, and the Young Modulus

  2. Turbulent + Laminar Flow • Laminar /Streamline Flow– layers do not cross each others paths. Occurs at lower speeds. • Turbulent Flow – layers cross and mix. Occurs at higher speeds.

  3. Viscous Drag Force • The force of friction caused by a flowing fluid • Is in the opposite direction to movement

  4. Upthrust Force • Upthrust is a force that acts vertically upwards on an object in a fluid • Upthrust = weight of fluid displaced

  5. Density • A measure of how close-packed the particles are in a substance. EG: gases are much less dense than solids and liquids because their particles are more widespread.

  6. Terminal Velocity • As an object falls it’s speed increases. The drag on it will also increase. Eventually a speed is reached where the drag force = the weight. As there is no net force on the object, the acceleration will be zero.

  7. Viscosity • The higher the viscosity of a fluid, the slower it flows. • Viscosities of most fluids decrease as the temperature increases. Fluids generally flow faster if they are hotter.

  8. Stokes’ Law • Calculates the drag force on a sphere as it travels through a fluid. • F = viscous drag force acting on the sphere • r = radius of the sphere • n = viscosity of the fluid • v = velocity of sphere

  9. ALL Forces on a Falling Sphere Stokes’ Law + Upthrust = Weight

  10. Hooke’s Law • The extension of a sample of material is directly proportional to the force applied. • Hooke’s Law does not apply to all materials • k = stiffness = the gradient = F/x

  11. Force v Extension/Compression Graphs • Limit of Proportionality – The point beyond which force is no longer directly proportional to extension (line is no longer straight) • Elastic Limit – This is when the force is taken away, the material no longer goes back to its original length • Yield Point – Material shows a greater increase in extension for a given increase in force • Ultimate Tensile Stress – The maximum stress that the material can withstand • Breaking Stress – the point at which the material breaks

  12. Ultimate Tensile Strength: the maximum stress (force) a material can withstand. • Breaking Stress: the stress at which the material breaks. Can be the same as UTS.

  13. Stress and Strain • Stress (N/m2) = Force (N) / Area (m2) • Strain (no units) = Extension (m) / Original Length (m)

  14. Young Modulus YM = Stress/Strain YM = (F/A)/(E/L) YM = FL/EA • YM = the gradient of a stress/strain graph • The greater the YM (the steeper the gradient) the stiffer the material. Ie: the less it stretches for a given force.

  15. Elastic and Plastic Deformation • At point A, Masses (Force) are unloaded from the material. • Plastic deformation has occurred as the material has not gone back to it’s original length.

  16. Material Characteristics • Brittle: Breaks suddenly without deforming plastically. Follows Hooke’s Law until it snaps. Glass. • Ductile: Undergos plastic deformation by being pulled into wire. Retains strength. Copper. • Malleable: Undergos plastic deformation by being hammered or rolled into shape. Loses strength. Gold. • Hard: Resist plastic deformation by compression or scratching rather than stretching. Diamond. • Stiff: Measure of how much a material stretches for a given force. Bamboo. • Tough: Measure of the amount of energy a material can absorb before it breaks. Toffee.

  17. Elastic Strain Energy • Plastically deformed material: • E = ½ x Force x Extension (Similar to W=Fs) • Elastically deformed material: • E = area under force/extension graph

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