Eat Flashcards
Viscosity
the flow of a liquid, how fast a liquid flows
Low viscosity
runny
High viscosity
sticky, thick
Laminar Flow
At low velocities a fluid tends to flow without lateral mixing and adjacent layers slide past one another - liquid is streamlined, no abrupt changes in direction or speed
Stoke’s Law relies on
Laminar flow
Turbulent flow
different layers of fluid cross over and mix, there is changing speeds and directions and little eddies are formed throughout the path - this occurs when the rate of flow reaches a critical level or an obstacle is in the way
Thixotrophy
Normally it doesn’t flow but when a force is exerted on it the viscosity lessens and it flows. When the force is again removed the viscosity increases and it stops flowing again (e.g. margarine)
Negative thixotrophy
normally it flows but when a force is exerted on it it hardens
How to measure flow rates?
measure mass (mass flow rate) or volume (volume flow rate) collected in a time interval
Hard material
a material that is not readily scratched or indented (e.g. diamond)
Stiff material
- doesn’t easily change shape when a force is applied - large load causes small deformation
- doesn’t extend much (e.g. steel)
Elastic material
- retains original shape when stretched
- when an object returns to its original shape after the load is removed (e.g. rubber)
Plastic material
- extends irreversibly
- when an object is deformed and doesn’t return to its original shape after the load is removed
Ductile material
-can be drawn into wires (e.g. copper)
Malleable material
- can be deformed and moulded into shape with a force
- can be hammered into sheets (e.g. gold)
Strong material
- large force is required to make it break
- high breaking stress (e.g. steel)
Brittle material
- little force is required to crack and break it
- no plastic deformation (e.g. glass)
Tough material
- requires lots of force to break
- high energy density (e.g. mild steel, rubber tyres)
Forces on a falling/rising ball bearing through a fluid
Upthrust, Viscous Drag, Weight
Viscous drag force
described by the relationship known as Stoke’s law
Archimede’s principle
the size of the upthrust on the ball bearing - buoyancy force on an object in a fluid is equal to the mass of the displaced fluid
How does temperature affect the viscosity?
the higher the temperature the lower the viscosity
Why are small objects used to test viscous drag and viscosity?
because larger objects have a big enough drag that it can’t be ignored unlike the drag on smaller objects
Viscous drag
- particles move past each other with different velocities, frictional forces between them can slow the flow
- size of the force depends on the viscosity of the fluid
Weak material
-low breaking stress (e.g. polystyrene)
Flexible material
-has a low young modulus (e.g. natural rubber)
Soft material
-surface is easily scratched (e.g. plastic)
Hooke’s Law
Force is proportional to the extension
Tensile
forces stretch the spring
Compressive
forces squash the spring
How would you identify a stiff material on a force extension graph?
There would be a straight line - the steeper the line the stiffer the material
How would you identify a plastic material on a force extension graph?
The line would curve
What regions can be identified on a force extension graph?
- elastic region
- elastic limit
- limit of proportionality
- plastic deformation
- break point
What is the limit of proportionality on a force extension graph?
the point where the material is still elastic and will return to its original shape but doesn’t act normally
What is the elastic limit?
where the material turns from elastic to plastic so no longer returns to its original shape
What is the break point?
the end of the line - the force will cause the material to break
Where is the plastic deformation?
where the line begins to curve
Stress
force per unit area
Strain
ratio of extension to original length
Refraction
as light/ a wave passes through a boundary into a more/less dense material it will change speed causing it to change direction
Polarization
light goes in all directions however when a polarizing lens is used it blocks the light in one plane (going in one direction)
Polarized glasses
stop light going in one plane, reducing the amount of light going into your eye
Magnetic field
a region in which a magnet experiences a force - its direction is that in which the north seeking pole of a needle would point
Electric field
a region in which a charged particle experiences a force - its direction is the direction of the force on a positively charged particle
Electromagnetic waves
electric and magnetic waves - oscillate at 90° to each other and the direction of travel
Which waves can be plane polarized?
only electromagnetic can be plane polarized and are affected by a polarizing filter - not longitudinal
Polarizing filters angle
work at 90° to each other
