Physical Science:

Anything that occupies space and has some mass is called matter. Everything around us is made up of matter. Matter can exist in three different forms depending on the conditions. These different forms of matter are also called the phases (or states) of matter. They are solid, liquid, or gas. On earth, water can exist in all three states at natural temperature. Ice is the solid form of water, water itself is in liquid form, and vapor is the gaseous state of water. Solid: has definite shape and size (volume). Particles in a solid have strong bonds between each other. The particles in a solid can vibrate but the structure does not not change. Metals and wood are some examples of a solid. Liquid: has a definite size (volume) but does not have definite shape. Liquid takes the shape of the container it is in. Particles (molecules) in a liquid are more spread out and can move around and bump into each other. Water and oil are some examples of liquid. Gas: neither has a definite size (volume) nor has a definite shape. Gas also takes the shape of the container it is in, and you can compress more gas into the same container. Particles (molecules) in a gas are far apart and can move around freely and quickly. Steam and air are some examples of gas.

Heat: we feel hot when we stand outside on a scorching summer day and we feel cold when touching an iron bar in the morning of a severe winter day. Such a sensation of hotness and coldness is called heat. Heat is a form of energy that can transfer from one location to another because of the temperature difference. A quantitative measure of the sensation of hotness or coldness is given by temperature. Therefore, temperature is the relative measure of hotness or coldness of a body. Heat energy is produced at the expense of mechanical energy and vice versa. For example, rubbing palms vigorously makes the palms warmer. Work and heat both transfer the energy from one system to another but temperature plays no role in transfer of energy due to work. Objects can store heat (or thermal energy) because the atoms and molecules of the objects are jostling around and bumping onto one another. This type of thermal energy is called an internal kinetic energy of the materials. The energy also arises in molecules due to intermolecular attractions. This type of energy is called an internal potential energy. During phase change of a material heat is stored in the form of internal potential energy. For example, heating of ice melts it without any rise of temperature. This energy is used in driving the molecules of ice away from each other against their molecular attraction. While internal energy refers to the total energy of all the molecules within the object, heat is the amount of energy flowing from one body to another spontaneously due to their temperature difference. Heat is energy in transit but not a property of the system. To measure how hot or cold something is, we use an instrument called a thermometer. Hence, the thermometer is a device used to measure temperature. The definition of temperature is not very straight forward to explain but the degree of hotness or coldness of a body would suffice as the definition for now. At the molecular level, temperature is the average kinetic of the molecules of a substance, whereas heat is energy in transit because of temperature difference. Hence, there is no notion of heat in a body. When heat is added to a body, internal energy of the molecules of the body increases and when heat is lost by the body its internal energy decreases. Since heat is a form of energy its SI unit is Joule (J), but the common unit of heat is calorie (cal) . A calorie is defined as the amount of heat necessary to raise the temperature of one gram of water to one degree Celsius at normal temperature and pressure (NTP).

Different materials behave differently to heat. Most materials increase their volume when heated, but there are some exceptional materials which shrink their volume on heating. For example: glass, steel, concrete, brass, etc. expand on heating or in rise of temperature. But welding iron, invar, etc. shrink volume on heating. Water on the other hand can shrink its volume when heated from \(0 \,^oC\) to \(4 \,^oC\) and expands after heating beyond that temperature. Such property of water is called an anomalous behavior of water. Due to this property of water aquatic animals survive when a pond is frozen in the winter.