Transcript Upthrust Force

Materials
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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.
• Turbulent Flow – layers cross and mix. Occurs at
higher speeds.
Viscous Drag Force
• The force of friction caused by a flowing fluid
• Is in the opposite direction to movement
Upthrust Force
• Upthrust is a force that acts vertically upwards
on an object in a fluid
• Upthrust = weight of fluid displaced
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.
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.
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.
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
ALL Forces on a Falling Sphere
Stokes’ Law + Upthrust = Weight
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
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
• 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.
Stress and Strain
•Stress (N/m2)
= Force (N) / Area (m2)
•Strain (no units)
= Extension (m) / Original Length (m)
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.
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.
Material Characteristics
1. Brittle: Breaks suddenly without deforming plastically.
Follows Hooke’s Law until it snaps. Glass.
2. Ductile: Undergos plastic deformation by being pulled
into wire. Retains strength. Copper.
3. Malleable: Undergos plastic deformation by being
hammered or rolled into shape. Loses strength. Gold.
4. Hard: Resist plastic deformation by compression or
scratching rather than stretching. Diamond.
5. Stiff: Measure of how much a material stretches for a
given force. Bamboo.
6. Tough: Measure of the amount of energy a material
can absorb before it breaks. Toffee.
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