# Listen and Learn Science/States of Matter
## Matter

Science considers that any observable physical object, which has mass and volume, as matter. Recent discoveries, have thrown up, many new interesting questions, regarding matter. But to start with, we will use, the conventional definition of matter.

## System of Units

Measurements have to be done in a standard way. Standards provide a common way of understanding, for all of us. The International systems of units, is a modern form of the metric system. It is abbreviated as the S I Units. It is used widely, Internationally. The S I System uses the M K S System, for the basic measurements. m stands for metre, which is used to measure length. k stands for kilogram, which is used to measure mass. s stands for second, which is used to measure time.
The c g s System, is a variation of the metric system. This is also widely used. c stands for centimetre, which is used to measure length. g stands for gram, which is used to measure mass. s stands for second, which is used to measure time. The c g s system is very much compatible with the S I system. It just uses smaller units. Centimetre instead of meter, for length. Gram instead of kilogram, for mass. The c g s system, is easily convertible to the S I system and vice versa. For example, 100 cm is equal to 1 m. 1000 grams is equal to 1 kg.

## Mass

All matter has mass. The S I Unit for mass is kilogram or kg. 1 kg is equal to 1000 grams. We use then word weight, interchangeably with mass. If we wish to express, our weight in Newtons, we need to multiply mass by acceleration. The Earth exerts an attractive force, on all matter, near it. This is called as a force of Gravity. This force is uniform through out the Earth. The acceleration caused due to the force of gravity, is called ‘g’. The value of acceleration ’g’, caused by Earth’s gravity is 9.8 m/s. If we have a mass of 50 kg, and wish to express the weight in Newtons, it will be equal to 50 multiplied by 9.8 is equal to 491 Newtons. So the weight of a person, with a mass of 50 kg, on Earth will be 491 Newtons. since the force of gravity is uniform through out Earth, we do not use Newtons to express weight. We conveniently, and some what loosely express our weight as 50 kg. Of course, our weight would be different in the moon. This is because, the moon’s gravity is much less than the Earth’s gravity. The same person weighing 491 Newtons on Earth, will weigh only 81.5 Newtons in the moon.

## Volume

All matter has volume. Volume is a 3 dimensional space. The S I unit for volume is cubic metre cube. The litre is also a metric unit, for measuring volume. A litre is 10 cm cube. That is, a litre is is equal to 1000 cubic centimetre. We normally abbreviate a cubic centi metre as cc. So, a litre is equal to 1000 cm cube, or cc. Smaller volumes is measured in millilitres, or ml. One millimetre is equal to one thousandth of a litre. That is, one litre is equal to 1000 millilitres, or ml. One milli litre is equal to one cubic centimetre. One ml is equal to one cc. One cubic metre is equal to 1000 litres. Depending on how much volume we are measuring, we can use cubic metre, or we can use litre. or we can use millilitres, or ml.

## Density

Density is mass per unit volume. We use the Greek letter rho, to represent density. Density is equal to mass divided by volume. Is equal to M by V. The S I Unit for density is kilo gram per cubic metre, which is expressed as kg per cubic metre. The c g s unit for density, is gram per cubic centimetre (cc). Cubic centimetre can also be called a milli litre. The Density of water, at 4 degrees Celsius is one gram per cc. The Density of Iron, is 7.8 grams per cc. The Density of Air, is 0.00198 grams per cc.

## Specific gravity

Specific gravity is used to measure the relative density of a substance. The standard substance used is water. We measure, the density of substances, relative to the density of water. Specific gravity is equal to, Density of the substance, divided by the Density of water. Specific gravity is a ratio, of the same units. So specific gravity has no unit or is dimensionless. Since the Density of water is one gram per centimetre cube, specific gravity, is numerically equal to Density. The Specific gravity of water, is 1. The Specific gravity of Iron, is 7.8. The Specific gravity of air is 0.00198.

## States of matter

Matter can exist, in one of the four possible states. Matter can be as a solid, liquid, gas, or plasma. These states of matter, can also be called the phase of the matter. The same substance, can change its phase, from one to another. For example, liquid water, can change to solid ice, or gaseous water vapour.

## Solid

A Solid is a state of matter, which is structurally rigid. A Solid resists changes to its shape or volume. The atoms in a solid, are tightly bound to each other. Usually the structure of binding, is geometrically symmetric. In some cases, the solid has a crystalline structure. Some examples of solids with a crystal structure are Diamond, salt and sugar. Most inorganic solids are poly crystals. When many microscopic crystals fuse together, they are called polycrystals. Most metals have a polycrystalline structure. Rocks and ceramics are also examples of polycrystalline substances. When the solid does not have a geometrically symmetric bonding, it is said to have a amorphous structure. Glass, wax, plastics are examples of solids, which have a amorphous structure. The atoms in a solid, are not stationery. They keep vibrating. The vibrations are at an atomic level. Because the vibrations are at an atomic level we cannot see these vibrations. These vibrations have kinetic energy. The extent of these vibrations can change. When we apply heat energy, the vibrations increase.

## Solid Mechanics

Engineers who work with solid structures, are interested in the mechanical properties of solids. Some of these properties are: tensile strength. This is the resistance of the solid, to being stretched. compressive strength. This is the resistance of the solid, to being compressed. elasticity this is the tendency of the solid, to return to its original shape when deformed, for example, when we stretch and release a rubber band, it returns to its original shape.
fracture toughness. This is the resistance to crack. We commonly refer to it as brittleness. For example, glass is brittle. It is prone to cracking.
Malleability. The ability to deform, without fracture or cracking. For example, gold is very malleable. This property makes gold amenable, to making jewellery.
This and other mechanical properties, are very important for engineering applications. When designing structures, machinery and appliances. Engineers make use of many of these properties.

## Thermal Properties

Solids also have thermal properties, conductivity, specific heat, latent heat, etc. Engineers use these properties also, while designing.

## Liquid

A liquid is not structurally rigid. The atoms are not as closely bound, as in a solid. The atoms have greater freedom to move around. Liquids flow and take the shape of the container. The atoms in a liquid also vibrate. When heat is applied, the vibrations increase. Unlike solids, this causes the liquid to move around. For example, when water is heated, on a stove, the warmer water tends to flow up. The cooler water tends to flow down. This causes, a convection current, in the boiling water. This convention current is visible to us. When more heat is applied, liquids evaporate and become gas.

## Gas

A gas has no structural rigidity. The atoms are not bound to each other. A gas in a container will defuse, and occupy all parts of the container. For example, the air in the room , where you are sitting, occupies the whole room. The atoms in the gas have more kinetic energy. The individual atoms move around freely. For example, if we light a candle, the smoke from the candle, will defuse, and spread through out the room. When heat is applied to the gas, the kinetic energy of the atoms increase, and the gas expands.

## Plasma

When a gas is ionized, the electrons separate from the atom. In such a state, the gas becomes a plasma. For example, in a neon lamp or a tube light, the gas is ionized. Ionized gas, allows electricity to be conducted. This is how a tube light works. Plasma state does not occur commonly in nature, in earth. We may not be aware of the plasma state. We may be surprised to know that most of the matter, in the universe is in a plasma state. This is because, all the gases in the stars, are in a plasma state. There are an estimated 300 sextillion stars in the universe. Knowing this we will probably appreciate that plasma is also, an important state of matter

## Phase change

A substance, can change from one state to another. This is called as a phase change. Heat plays a primary role, in the change of state, of a substance. Water in its natural state, is a liquid. When Water is heated, to 100 degrees Celsius, it evaporates, to become a gas, we call as water vapour. When water is cooled, to 0 degree Celsius, it becomes solid ice. So, water can exist, as a solid, liquid, or gas. When a substance is heated, basically the molecules in the substance, get excited. The molecules start vibrating. This vibration can happen in many dimensions, depending on whether, they are in a solid, liquid, or gaseous state. When the molecules are excited, they have more kinetic energy.Heat basically increases the kinetic energy of the molecules of the substance.
When a liquid is heated, it becomes a gas. The temperature at which, a liquid becomes a gas, is called the boiling point. When a liquid is cooled, it becomes a solid. The temperature at which a liquid becomes a solid is called the freezing point. When a solid is heated, it melts to become a liquid. The temperature at which, a solid becomes a liquid, is called the melting point. The boiling point, melting point, and freezing point, is different for different substances.
Water in its natural state, is a liquid. It has a boiling point of 100 degree Celsius (°C). It has a freezing point of 0 °C.
Iron in its natural state, is a solid. The melting point of Iron is 1538°C. When heated to this temperature, Iron becomes a liquid. In a furnace, where iron is manufactured, it is in a liquid state. It is normally cast into moulds. On cooling to room temperature, it becomes a Solid. The boiling point of iron is 2861°C. When heated to this temperature, iron becomes a gas. In many stars, Iron and many metals, exists as a gas.
Oxygen in its natural state, is a Gas. The boiling point of Oxygen, is -183°C. When Oxygen is cooled to -183°C, it becomes a liquid. Liquid Oxygen is used for medical purposes. It is also carried by climbers at high altitudes, and under water divers. The boiling point of Oxygen is -219°C. When oxygen is cooled to -219°C it becomes a solid.
The natural state of a substance can be solid, liquid or gas but it can be changed to another state, by heating or cooling.