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Ultrasonic welding

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Thermodynamics: Basic Terms

Thermodynamics:  The branch of science that deals with the study of different forms of energy and the quantitative relationships between them.

System:  Quantity of matter or a region of space which is under consideration in the analysis of a problem.

Surroundings:  Anything outside the thermodynamic system is called the surroundings. The system is separated from the surroundings by the boundary. The boundary may be either fixed or moving.

Closed system:  There is no mass transfer across the system boundary. Energy transfer may be there.

Open system:  There may be both matter and energy transfer across the boundary of the system.

Isolated system:  There is neither matter nor energy transfer across the boundary of the system.

State of the system and state variable:  The state of a system means the conditions of the system. It is described in terms of certain observable properties which are called the state variables, for example, temperature (t), pressure (p), and volume (v).

State function:  A physical quantity is a state function in the change in its value during the process depends only upon the initial state and final state of the system and does not depend on the path by which the change has been brought about.

Macroscopic system and its properties:  If as system contains a large number of chemical species such as atoms, ions, and molecules, it is called macroscopic system. Extensive properties: These properties depend upon the quantity of matter contained in the system. Examples are; mass, volume, heat capacity, internal energy, enthalpy, entropy, Gibb's free energy. Intensive properties:  These properties depend only upon the amount of the substance present in the system, for example, temperature, refractive index, density, surface tension, specific heat, freezing point, and boiling point.

Types of thermodynamic processes:  We say that a thermodynamic process has occurred when the system changes from one state (initial) to another state (final).

Isothermal process:  When the temperature of a system remains constant during a process, we call it isothermal. Heat may flow in or out of the system during an isothermal process.

Adiabatic process:  No heat can flow from the system to the surroundings or vice versa.

Isochoric process:  It is a process during which the volume of the system is kept constant.

Isobaric process:  It is a process during which the pressure of the system is kept constant.

Reversible processes:  A process which is carried out infinitesimally slowly so that all changes occurring in the direct process can be exactly reversed and the system remains almost in a state of equilibrium with the surroundings at every stage of the process.

Exothermic Process:

Process that releases heat to its surroundings.

Energy:

Capacity for doing work or supplying heat

Calorie:

Quantity of heat needed to raise the temperature of 1 gram of pure water by 1 degree C

Conversion used to go between calorie and joule

4.184 J=1 calorie

SENSIBLE HEAT VS LATENT HEAT

Two forms of heat are relevant in air conditioning:

• Sensible heat
• Latent heat

Sensible heat

When an object is heated, its temperature rises as heat is added. The increase in heat is called sensible heat. Similarly, when heat is removed from an object and its temperature falls, the heat removed is also called sensible heat. Heat that causes a change in temperature in an object is called sensible heat.

Latent heat

All pure substances in nature are able to change their state. Solids can become liquids (ice to water) and liquids can become gases (water to vapor) but changes such as these require the addition or removal of heat. The heat that causes these changes is called latent heat.

Latent heat however, does not affect the temperature of a substance - for example, water remains at 100°C while boiling. The heat added to keep the water boiling is latent heat. Heat that causes a change of state with no change in temperature is called latent heat.

Stress on an Inclined Plane.MP4

Stress on an Inclined Plane.MP4

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lower centre of gravity -application

Every single body and thus the athletes themselves, is made up of individual components each of which has its own weight. So our weight is just the sum of individual weights, of components such as our arms, legs, etc. The point, about which the distribution of these individual weights is symmetrical, is the center of gravity of the body. Thus, if a body has more mass distributed in its upper part, the center of gravity will be closer to the top of the body. This applies to humans, as the center of gravity of an average person is located approximately at a height of one meter, thus being above the waist

There are two properties of the center of gravity that have a great impact on sport. First of all its location is dependent on the shape of the body. So if the same body is to take a different shape, the position of the center of gravity will shift. An athlete that bends his/her legs will lower his/her center of gravity position. This, amongst other things, will result in greater stability, something especially important in sports such as wrestling. Also, and this may sound the strangest, the center of gravity can lie entirely outside the body itself. For example, if the body is hollow it will literally be positioned somewhere in the air. During the Olympic Games in Mexico, in 1968, an, until then unknown athlete, the American Dick Fosbury, came from nowhere to teach the world about both of these properties.

The truly ingenious leap (!) in the technique was that by clearing the bar with his back and by changing the shape of his body, the athlete could clear the bar without his center of gravity having to also clear it. By this change in body shape he was able to move his center of gravity outside his body. The energy required for a jump depends on the maximum height of the center of gravity and so by lowering its position one also lowers the energy required to clear the bar