GLOSSARY OF BASIC TECHNICAL TERMS - Physics

Acceleration: The acceleration of an object is its change in velocity per unit time in the direction of change. It is a vector with direction and magnitude. Unit is m /sec.2

Conduction: It is the transfer of heat energy from one region to another region through a substance with out the movement of the substance as a whole is known as conduction. It is the transfer of heat from particle to particle in a substance. Some materials are good conductor and some are bad conductor of heat.

Convection: It is the transfer of heat by the substance moving en bloc. Heated substance (gas or liquid) loses density and therefore rises (moves) to cooler region in the substance. Heated substance looses density, therefore moves from hot region to cooler region and colder substance (with higher density) move to towards the source of heat. Hence a convection current is set up.

Creep: A time dependent strain of solid resulting from stress.

Density: It is mass per unit volume. Unit is gr/cc or kg / m3 .

Efficiency: It is defined as the ratio of work got out to work put in. It is important to cut down the energy wasted so that the useful work obtained from a machine is as high as possible.

Energy: A body capable of doing work is said to posses energy. See also Work. A body may be capable of doing work because it is moving or because of its state or position. Unit is kg. .m or Nm. Since there are many different ways in which a body may be capable of doing work, there are different forms of energy like Mechanical energy, Electrical energy, Chemical energy, Heat energy, Nuclear energy, etc.

Fatigue: Weakness in metal caused by repeated stress in metal is known as fatigue.

Flexural Strength: It is the measurement of resistance of the material to fracture during bending.

Force: Force is not visible but its effect is visible. Force is rate of change of momentum. Momentum is product of mass and velocity.

Force = mass x acceleration. It has a direction and a magnitude. Unit is kg.m/sec2 . 1 kg = 10N.

Heat: It is a form of energy. Its unit is Calorie. It is related to temperature by

Heat = mass x specific heat x temperature difference.

Hydraulic Pressure: Pressure exerted in the hydraulic system. Hydraulic injection pressure is not same as pressure on melt at screw tip. Hydraulic pressure is required to be multiplied with intensification ratio to get pressure on melt at screw tip.

Integrated Circuit: It is a complete miniaturised electronic circuit that has been etched in to a small silicon wafer or chip.

Isotropic: It means that the material is having same properties regardless of the direction of measurement.

Isothermal: When the temperature is kept constant during the change in pressure and volume by adding or removing heat energy from the system, it is called isothermal process.

Similarly when heat content of the system is kept constant therefore temperature alone is altered with out entry or exit of heat, then the process is called adiabatic.

Latent Heat: When a substance changes fri4om one state to another energy is either absorbed or liberated. This heat energy is called the Latent heat. The specific latent heat is the energy required to change the state of 1kg of the substance. The specific latent heat of fusion is the heat energy required to change 1 kg of material in the solid state at its melting point to 1kg of the material in its liquid state, and that released when 1kg of the liquid changed to 1kg of solid.

No Flow Temperature: No flow temperature is the temperature at which the viscosity of the melt is so high that it effectively can not be made to flow.

Power: It is rate of doing work. The rate at which energy is used. The ratio of work done to the time taken. Unit is Watt. 1 watt = 1 joule per sec. Or kg.m / sec.

Pressure: It is the normal (perpendicular) force acting on unit area. Unit is kg/cm2 (Bar) or N/m2 (Pascal).

Pressure Drop: Pressure drop is the loss of pressure that occurs when the melt is pushed into a section of the mould during the filling phase.

Radiation: Heat transfer by Radiation takes place in the form of electromagnetic wave. These waves do not need medium for transfer. Heat radiation has a range of wave length. Heat from Sun reaches the earth by radiation.

Rheology: Rheology is defined as a science concerned with the laws of deformation of various materials.

Shrinkage: It is the deviation of dimensions of the moulded part from the dimensions of cavity when measured on moulded part after certain hours. Compressibility, thermal expansion and pvT characteristics influence the dimensions of moulded part.

Specific Heat: Temperature is measure of heat energy level whereas heat is a measure of total internal energy contained in a body. When the same quantity of heat is given to equal masses of different substances, they do not result in the same rise in temperature. The specific heat is defined as the quantity of heat energy which will rise the temperature of unit mass (1kg) of a substance by 10C. Heat = mass x specific heat x Temperature rise.

Specific Volume: It is inverse of density. It is volume per unit weight. Unit is cc/gr.

Temperature: Temperature is measure of heat energy level whereas heat is a measure of total internal energy contained in a body. Unit is 0C.

Thermal Properties: Thermal properties describe how a given polymer will behave during the exchange of heat. They are important factor in determining how succeptible a material is to shear heating; they also characterise how quickly a given polymer will cool down.

Thermal Stability: It is polymers thermal characteristic. It is the time interval for which polymer remains stable at certain temperature. Beyond that time if the polymer is exposed to longer duration for a given temperature, it degrades.

Thermal Conductivity: It is defined as the rate of flow of heat between two surfaces of unit area sepated by unit distance when the temperature difference between them is 10 C.

Tolerance: The amount of variation in a dimension that may be permitted without impairing the functional fitness of the part. The maximum and minimum dimensions defining the boundaries of the tolerance zone is known as limits.

Velocity: The velocy of an object is its displacement per unit time. In the direction of displacement. It has a direction and a magnitude. Unit is m / sec. Or cm / sec.

Viscosity: Viscosity is a way to describe how much resistance a melted polymer exhibits when an attempt is made to make it flow. High viscosity means the melt is thick and resistance to flow is high. Low viscosity means resistance flow is less.

It is the internal resistance to flow existing between two liquid layers when they are moved relative to each other. This internal resistance is a result of interaction between liquid molecules in motion.

Warpage: Uneven bending, Twisting etc on account of differential cooling, differential shrinkage, or non uniform freezing of melt in the mould can cause these conditions in the moulded part.

Work Done: Work is said to be done if an unbalanced force moves its point of application through a distance measured in the direction of force. Work = Force x Distance.

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