# Physics on the go

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## Stress/ Strain graphs

- limit of proportionality - the point after which the line stops being straight (stress proportional to strain up to this point). the material is still behaving elastically and will return to its original length when the deforming force is removed.
- elastic limit (occurs between limit of proportionality and yield point): wire stops behaving elastically and starts to behave plastically
- yield point - material shows appreciably greater increase in strain for a given increase in stress
- highest point on stress-strain graph - ultimate tensile strength - the maxximum stress that can be applied before a sample breaks

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## young modulus

- gradient of stress-strain curve = young modulus
- units Nm-2 or Pa

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## Materials

- Brittle - break with little or no plastic deformation
- malleable - can be beaten into sheets; shows large plastic deformation under compression
- ductile - can be pulled into wires or threads; these materials show plastic deformation before faliure under tension
- hard- resist plastic deformation by surface indentation or scratching
- tough - can withstand impact forces and absorb a lot of energy before breaking; large forces produce a moderate deformation

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## Viscosity and viscous drag

- fluid layers experience friction forces between each other
- this causes viscous drag ( a cause as air resistance)
- viscous drag - depends on type of fluid as well as shape of object and type of fluid flow.
- in a material where viscous drag would be higher, the viscosity is greater.
- units of viscosity:
- viscosity of liquid : decreases with temperature
- viscosity of gas: increases with temperature

Stokes' law gives formula for viscous drag for small sphere at low speeds in laminar flow.

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## Viscosity and viscous drag

- fluid layers experience friction forces between each other
- this causes viscous drag ( a cause as air resistance)
- viscous drag - depends on type of fluid as well as shape of object and type of fluid flow.
- in a material where viscous drag would be higher, the viscosity is greater.
- units of viscosity:
- viscosity of liquid : decreases with temperature
- viscosity of gas: increases with temperature

Stokes' law gives formula for viscous drag for small sphere at low speeds in laminar flow.

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## Viscosity and viscous drag

- fluid layers experience friction forces between each other
- this causes viscous drag ( a cause as air resistance)
- viscous drag - depends on type of fluid as well as shape of object and type of fluid flow.
- in a material where viscous drag would be higher, the viscosity is greater.
- units of viscosity:
- viscosity of liquid : decreases with temperature
- viscosity of gas: increases with temperature

Stokes' law gives formula for viscous drag for small sphere at low speeds in laminar flow.

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## Viscosity and viscous drag

- fluid layers experience friction forces between each other
- this causes viscous drag ( a cause as air resistance)
- viscous drag - depends on type of fluid as well as shape of object and type of fluid flow.
- in a material where viscous drag would be higher, the viscosity is greater.
- units of viscosity:
- viscosity of liquid : decreases with temperature
- viscosity of gas: increases with temperature

Stokes' law gives formula for viscous drag for small sphere at low speeds in laminar flow.

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## Viscosity and viscous drag

- fluid layers experience friction forces between each other
- this causes viscous drag ( a cause as air resistance)
- viscous drag - depends on type of fluid as well as shape of object and type of fluid flow.
- in a material where viscous drag would be higher, the viscosity is greater.
- units of viscosity:
- viscosity of liquid : decreases with temperature
- viscosity of gas: increases with temperature

Stokes' law gives formula for viscous drag for small sphere at low speeds in laminar flow.

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## Terminal velocity

- when resultant force = 0 , downwards acceleration = 0.
- this is terminal velocity.

measuring viscosity :

drop ball bearing through fluid. voscous drag, and hence viscosity, can be measured.

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## Elastic strain energy

- work can't be found from f x distance in direction of force as force isn't constant.
- 1/2 f x delta x is average force x distance

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