Heat is probably the easiest energy you can use to change your physical state. The atoms in a liquid have more energy than the atoms in a solid. There is a special temperature for every substance called the melting point. When a solid reaches the temperature of its melting point, it can become a liquid.

Freezing is the reverse process to melting. To cause freezing energy must be removed. Because you are removing heat to freeze a substance it is called a exothermic change. The point at which this happens is called the freezing point.

Adding or removing energy from matter causes a physical change as matter moves from one state to another. For example, adding thermal energy (heat) to liquid water causes it to become steam or vapor (a gas). When heat is applied to a solid, its particles begin to vibrate faster and move farther apart.

Physical conditions like temperature and pressure affect state of matter. When energy is removed, the opposite happens, decreasing the substance’s temperature and turning it from liquid to solid (freezing), gas to solid (deposition), or from gas to liquid (condensation).

Effect of Change of Pressure When we apply pressure and reduce temperature the gases can be converted into liquids i.e., gases will be liquefied. The process of conversion of a gas into a liquid by increasing pressure or decreasing temperature is called liquefication.

Changes in presure have very little effect on the volume of a liquid. Liquids are relatively incompressible because any increase in pressure can only slightly reduce the distance between the closely packed molecules. If the pressure above a liquid is increased sufficiently, the liquid forms a solid.

In a closed system where volume is held constant, there is a direct relationship between Pressure and Temperature. In a direct relationship, one variable follows the same change when it comes to increasing and decreasing. For example, when the pressure increases then the temperature also increases.

In areas with low temperature, the air is cold and heavy so, it sinks down. This creates a high pressure area. High pressure is associated with clear and sunny skies.

Pressure was defined to be force per unit area. This equation tells us that the pressure exerted by a column of water is directly proportional to the height of the column and the density of the water and is independent of the cross-sectional area of the column.

h is height. Thus water’s density can be more reasonably approximated as constant than that of air, and given the same height difference, the pressure differences in water are approximately equal at any height.

As altitude rises, air pressure drops. In other words, if the indicated altitude is high, the air pressure is low. As altitude increases, the amount of gas molecules in the air decreases—the air becomes less dense than air nearer to sea level.

Pressure within a liquid depends only on the density of the liquid, the acceleration due to gravity, and the depth within the liquid. Pressure within a gas depends on the temperature of the gas, the mass of a single molecule of the gas, the acceleration due to gravity, and the height (or depth) within the gas.

Density and pressure/temperature Density is directly proportional to pressure and indirectly proportional to temperature. As pressure increases, with temperature constant, density increases. Conversely when temperature increases, with pressure constant, density decreases.

With more particles there will be more collisions and so a greater pressure. Because the area of the container has increased, there will be fewer of these collisions per unit area and the pressure will decrease. Volume is inversely proportional to pressure, if the number of particles and the temperature are constant.

Pressure is the weight of the fluid mg divided by the area A supporting it (the area of the bottom of the container): P=mgA P = mg A . P=hρg P = h ρ g , where P is the pressure, h is the height of the liquid, ρ is the density of the liquid, and g is the acceleration due to gravity.

As water gets warmer, its molecules spread out, so it becomes less dense. This structure is less dense than the liquid water, so ice floats. Deep water is denser than shallow water. The water molecules are packed together more tightly because of the weight of water above pushing down.