There are three basic states of matter: solid, liquid, gas. Plasma (formed when the particles in a gas gain an electronic charge) and Bose-Eistein Condensate (formed when special gases are cooled to extremely low temperatures) are other forms of matter. Matter expresses its state by expressing its containership.
A solid is hard and keeps a definite shape because its tiny particles are packed closely together. The motion of these particles are restricted only to vibration in their alloted spaces (no movement over or around one another). This compactness is exemplified in crystaline solids where the particles that form the solid are arranged in a regular repeating pattern called a crystal (e.g sodium chloride, commom salt).
The particles of a liquid are not as closely packed together as those of a solid. So, they are less rigid in their respective spaces and have freedom of movement. Consequently, a liquid has no definite shape. It takes the shape of its container. However, a liquid has definite volume (the ratio of its mass to its density). This implies that it will occupy a space equal to its volume. So if the volume of the container is more than its volume, it will not fill up the container. If the volume of the container is less than its volume, it will overflow.
The freedom of movement of a liquid is basically expressed as a flow. The rate of flow of liquids vary. Liquids that flow slowly are viscous. The resistance of a liquid to flow is called viscosity (the slower the flow, the higher the viscosity). Some solids called Amorphous Solids do not have the cystalline structure. So, they are capable of slow flow. Consequently, they are sometimes referred to as slow flowing liquids (e.g glass).
A gas has neither a definite shape nor a definite volume (it fills all available space in a container). This is because the freedom of movement of the particles of a gas is naturally unrestrained. However, humans have devised various ways by which they can closely pack the particles of a gas inorder to restrict their inclination to spread-out and in reverse, unpack the particles in order to allow the particles to spread-out. These processes are respectively called the compression and expansion of gases.
When a gas is in a container, its propensity for motion is not eliminated. In fact, the particles of a gas in a container are in consistent motion and can attain a speed of about 100 meters per sec. This motion causes numerous constant collisions of particles with one another and the walls of the container. Consequently, there is an outward push or pressure exerted by the gas that allows it to fill its container. If the pressure in the container becomes too great and there is no opposite and equal pressure to conatin the gas, it will blow out. The behaviour of a given volume of gas with respect to pressure and temperature is sumarized by the gas laws. The gas laws comprises Boyle's law which states that the volume of a fixed amount of gas varies inversely with the pressure of the gas and Charles law which states that the volume of a fixed amount of gas varies directly with the temperature of the gas.
The containership of matter (i.e matter's residency), matter's various motions, the forces they exert, their various identities, their various groupings/interactions and the equilibriums they seek, are all expressions of Pj Problems.