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## PowerPoint Slideshow about ' States of matter' - roanna-mclaughlin

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zz

yz

xz

zy

zx

yy

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xy

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x

internal interactionIn a medium, a set of parameters leading to the forces exerted on an infinitesimal cube element within the medium, is called the stress tensor.

where is the i-th scalar component of the force exerted on the j-th wall of the cube and dA is the area of one wall.

The SI unit of stress is the pascal (Pa).

Note: Only six independent components.

dyz

dzz

dxz

dzy

dyy

y

dxy

dxx

dzx

dyx

x

deformationThe deformation is described by a strain tensor

where d(xi)j is the displacement of the j-th corner in the i-th direction, and is the size of the cube (initial).

Within certain limits, the differential change in stress, caused by external forces exerted on the medium, is a linear function of the differential strain.

or

Hook\'s lawThe proportionality tensor is called a modulus.

The external forces are applied along a single line to two opposite sides

F

L

L

The nonzero component of compressive stress is called uniaxial pressure (P)

y

-F

x

compression (uniaxial pressure)Tangential external forces applied to two opposite sides of the object cause a shear stress

dy

h

d

dF

y

-dF

x

Shear stressCoefficient S is called the shear modulus.

Comment 1. Fluids in rest do not create shear stress.

Comment 2. The occurrence of a velocity dependent stress in a moving fluid is called viscosity.

dF

Under hydrostatic pressure, all shearing components of the stress are zero and all compressive components of stress are equal.

dF

dF

dF

dF

x

y

Hydrostatic pressureHook’s law:

F0

h

W

In a gravitational field, pressure in fluids depends on the pressure created by an external force and the depth in the fluid

F(h)

fluid at restP0

for uniform density:

P(h)

Pascal\'s principle

A change in the pressure applied to an enclosed (incompressible) fluid is transmitted undiminished to every portion of the fluid.

F2

Hydraulic Press:

A1

A2

2

1

Archimedes\' principledA2

dA

dA1

A body submerged (partially or completely) in a fluid is buoyed up with a force equal in magnitude to the weight of the fluid displaced by the body

Ideal fluid

- nonviscous - there is no internal friction;
- flows steadily - at any point, the velocity of the fluid does not depend on time;
- incompressible - its density does not depend on pressure;
- irrotational - does not produce vortices

When the rate of flow is small (laminar flow), many fluids can be approximated by the ideal fluid.

For in ideal fluid, the sum of the pressure, the kinetic energy per unit volume, and the potential energy per unit volume has the same value at all points along a streamline.

Bernoulli\'s equationv2

y2

A2

dx2

v1

y1

A1

dx1

from the work-energy theorem:

Thermal contact

Two systems are in thermal (diathermic) contact, if they can exchange energy without performing macroscopic work.

This form of energy transfer (random work) is called heat.

1. Convection

natural convection:

resulting from differences in density

forced convection:

the substance is forced to move by a fan or a pump.

The rate of heat transfer is directly related to the rate of flow of the substance.

dQ = cTdm

E

Mechanisms of Heat Transfer

1. Radiation

Energy is transmitted in the form of electromagnetic radiation.

Stefan’s Law

= 6 10-8 W/m2K

A – area of the source surface

e – emissivity of the substance

T – temperature of the source

Zeroth law of thermodynamics

Thermal Equilibrium:

If the systems in diathermic contact do not exchange energy (on the average), we say that they are in thermal equilibrium.

If both systems, A and B, are in thermal equilibrium with a third system, C, then A and B are in thermal equilibrium with each other.

Temperature

We say that two systems in thermal equilibrium have the same temperature. (Temperature is a macroscopic scalar quantity uniquely assigned to the state of the system.)

Gas Thermometer

T3 = 273.16 K is the temperature at which water remains in thermal equilibrium in three phases (solid, liquid, gas).

The Celsius scale and, in the US, the Fahrenheit scale are often used.

;

l

D

dD

Thermal expansionFor all substances, changing the temperature of a body while maintaining the same stress in the body causes a change in the size of the body.

linear expansion:

dl = ldl

The proportionality coefficient (T) is called the linear thermal expansion coefficient.

volume expansion:

dV =VdV

The proportionality coefficient (T) is called the volume thermal expansion coefficient.

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