Chapter 12- Fluids Flashcards
Fluid is
A material that flows
Liquid or gas
Density eq
Mass/ volume
Symbol = rho ‘p’
Find density of air
Vacuum out air of a flask
De clip and put tube into water so it draws in water to replace air lost
Then you can see the density of the air
Pressure above you when swimming
Created by WEIGHT of water above you
Air pressure in atmosphere =
1.0 x10^5 Pa
Pressure in fluids eq
Pressure at base= weight of column/area = mg/A = Vpg/A
Volume of column (V) = Ah
Therefore
p= h’p’g
Upthrust =
Weight of the displaced fluid
Archimedes principle
States that when a body is totally or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced
Flotation
Will float if upthrust (weight of fluid displaced) is equal to weight of object
Example of flotation
A sea vessel must displace more of the less dense fresh water to balance its weight and so it lies deeper in fresh water than the salt water
Streamlines
Represent velocity of a fluid at each point within it
Drawn as arrowed lines showing paths taken by small regions of the fluid
Laminar flow
Occurs when adjacent layers of fluid do not cross into each other
Turbulent flow
Occurs when layers of fluid cross into each other, resulting in the formation of vortices or eddy currents
Viscosity
The ability of a fluid to flow
As in a high viscosity means it can’t flow (e.g. Syrup)
Which device to compare viscosity
Redwood viscometer
Stokes law def
States that for a sphere moving through a fluid, the viscous drag acting on it is given by the eq.
Provided the movement of the fluid relative to the sphere is laminar
How is viscous drag created on a sphere
Sphere moves slowly through a fluid
Movement of the fluid relative to the sphere is laminar
Molecules of the fluid adhere to the surface of the sphere and move along with it
Creating a viscous drag between the other layers of fluid
Terminal velocity
Reached when a body moving trough a fluid’s resultant forces acting on it equal zero
Terminal velocity eq
Fr = W - (U+F)
U+F = W
How to measure viscosity of a liquid
Falling ball bearing method
Measuring cylinder full of liquid
Time taken for it to fall between each level is taken
When timings become similar is when terminal velocity has been reached
Viscosity and temperature
When temp of fluid rises it’s internal energy increases. The adhesive forces between molecules and the cohesive forces at solid surfaces decrease causing a reduction in viscosity
Hot fluids become more ‘runny’
Thixotropy
Viscosity reduces as the rate of flow increases
I.e. Toothpaste when pressure is applied
