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States of matter (Solid, Liquid, Gas, Plasma)
States of matter (Solid, Liquid, Gas, Plasma)

States of matter

All the matter around us exists in different states. It means they all are varying with respect to appearance, physical form, chemical properties, interaction with each other, etc. Previously there were only three states of matter, but it has long changed to few more like plasma, Bose- Einstein condensate etc. Only main three states (solid, liquid, gas) and plasma are studied till the graduation.


In solid state the objects are rigid, as the individual particles (Atoms or molecules) are tightly packed.  The electrons of each atom are constantly in motion, so the atoms have a small vibration, but they are fixed in their position. Because of this, particles in a solid have very low kinetic energy. As a result, solids have fixed shape or definite volume. And it can be only changed by external force or pressure.

In crystalline solids, the particles are packed in orderly manner, in repeating matrix. There are various crystal structures, and the same substance can have more than one structure (or solid phase). For example, iron has a body-centred cubic structure at temperatures below 912 °C, and a face-centred cubic structure between 912 and 1394 °C. Ice has fifteen known crystal structures, or fifteen solid phases, which exist at various temperatures and pressures.

Glasses and other non-crystalline, amorphous solids without long-range order are not thermal equilibrium ground states; therefore, they are described below as nonclassical states of matter.

Solids can be transformed into liquids by melting and can also change directly into gases through the process of sublimation.


            SOLID                                LIQUID                                GAS   States_of_matter     


In liquids, the particles have a great deal of space between them, but not as great as gases (where the particles are free to move around). The particles in liquid are bound together but do not have a fixed shape. They take the shape of containers where they are placed in. It is nearly incompressible fluid and retains a (nearly) constant volume independent of pressure.
The volume of liquid is definite at same pressure and temperature. The volume of a liquid depends on both pressure and temperature.


A gas does not have a definite shape as the particles are not held together by strong forces and wander freely. In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighbouring molecules is much greater than the molecular size. A gas has no definite shape or volume but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature.


Plasma is very similar to gas in appearance and does not have a definite shape or size. Unlike gases, plasmas are electrically conductive, produce magnetic fields and electric currents, and respond strongly to electromagnetic forces. Positively charged nuclei swim in a "sea" of freely moving disassociated electrons, similar to the way such charges exist in conductive metal, where this electron sea allows matter in the plasma state to conduct electricity.

A normal gas can be converted to plasma by exposing it to very high voltage or very high temperature.

The plasma state is often misunderstood, and although not freely existing under normal conditions on Earth, it is quite commonly generated by either lightning, electric sparks, fluorescent lights, neon lights or in plasma televisions. The Sun's corona, some types of flame, and stars are all examples of illuminated matter in the plasma state.


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Thermodynamics can be defined as the science of energy. Energy can be defined as something which changes the physical property or chemical property of an object.

The word thermodynamics has been derived from Greek which means “heat power, which is the most descriptive of the earlier efforts to convert heat into power. Thermodynamics now is interpreted to include all aspects of energy and energy transformations, including power generation, refrigeration, and relationships among properties of matter.


The design of many engineering system involves thermodynamics as shown in this figure.

Thermodynamics is defined by different laws which are known as the laws of the thermodynamics. There are three laws.

Laws of the thermodynamics:

1st Law of the thermodynamics: it simply states that during an interaction, energy can change from one form to another, but the total amount t of energy remains constant. That is energy can never be created or destroyed.

This law is also known as the conservation of energy principle. For example: a rock falling from a height is simply the conversion of the gravitational potential energy into kinetic energy.

2nd Law of thermodynamics: It simply states that energy has quality as well as quantity and the actual process occur in the direction of decreasing quality of energy. For example, a cup of hot coffee left on the table eventually cools but a cold coffee left on the same table never heats up. The high temperature energy of the coffee is degraded (transformed into less useful form of energy) as I it is transferred to the surrounding air.


The heat flows in the direction from high temperature to low temperature

3rd Law of thermodynamics: The third law of thermodynamics states as follows, regarding the properties of closed systems in thermodynamic equilibrium:

The entropy of a system approaches a constant value as its temperature approaches absolute zero. At absolute zero the system must be in a state of least possible energy.

Zeroth law of the thermodynamics: It states that if two bodies are in thermal equilibrium with a third body, then they are also in thermal equilibrium with each other. Two systems can be said to be in thermal equilibrium with each other if they have the same temperature.



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Fuels (used to run engines)
Fuels (used to run engines)



Fuels are the source of energy that runs all the mechanical and electronic systems that we use and see all around us. There are many materials that can be used as fuels. For example: from earlier days wood, charcoal, dry leaves, dry dung cakes etc. were used as fuel to generate heat to cook food and boil water and keep oneself warm. Later coal was discovered, and it then was used as fuel and later on petroleum and later on electricity.