States of matter. Solid:. Fluid:. Liquid Gas Plasma. Crystalline Amorphous. z. zz. yz. xz. zy. zx. yy. yx. xy. y. xx. x. internal interaction.
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In 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.
Within certain limits, the differential change in stress, caused by external forces exerted on the medium, is a linear function of the differential strain.
The proportionality tensor is called a modulus.
Tangential external forces applied to two opposite sides of the object cause a shear stress
Coefficient 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.
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 equation
from the work-energy theorem:
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. Thermal Conduction
law of thermal conduction:
resulting from differences in density
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
Mechanisms of Heat Transfer
Energy is transmitted in the form of electromagnetic radiation.
= 6 10-8 W/m2K
A – area of the source surface
e – emissivity of the substance
T – temperature of the source
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.
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.)
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.
For 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.
dl = ldl
The proportionality coefficient (T) is called the linear thermal expansion coefficient.
The proportionality coefficient (T) is called the volume thermal expansion coefficient.