MATTER- Something that occupies space and can be perceived by one or more senses; a physical body, a physical substance, or the universe as a whole.
FORMS OF MATTER:
SOLID-In a solid the particles (ions, atoms or molecules) are packed closely together. The forces between particles are strong so that the particles cannot move freely but can only vibrate. As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by force, as when broken or cut.
LIQUID-A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if thetemperature and pressure are constant. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance.
GAS-A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container.
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 neighboring 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.
PHASES OF MATTER:
Matter can exist in four phases (or states), solid, liquid, gas, and plasma, plus a few other extreme phases like critical fluids and degenerate gases.
Generally, as a solid is heated (or as pressure decreases), it will change to a liquid form, and will eventually become a gas. For example, ice (frozen water) melts into liquid water when it is heated. As the water boils, the water evaporates and becomes water vapor.
Sometimes, a solid will go directly from solid to gas - this is call subliming. An example of sublimation is dry ice, the solid (frozen) form of carbon dioxide, CO2, which turns into gaseous carbon dioxide at standard...