`➢` In the previous section we have discussed mechanical energy. We have seen that it can be classified into two distinct categories : one based on motion, namely kinetic energy; the other on configuration (position), namely potential energy. Energy comes in many a forms which transform into one another in ways which may not often be clear to us.
`color{red} ► color {blue} bbul" Heat"`
`➢` We have seen that the frictional force is excluded from the category of conservative forces. However, work is associated with the force of friction.
`➢` A block of mass `m` sliding on a rough horizontal surface with speed `v_0` comes to a halt over a distance `x_0`.
`➢` The work done by the force of kinetic friction `f` over `x_0` is `–f x_0`.
`➢` By the work-energy theorem `m v_0^2 //2 = f x_0` . If we confine our scope to mechanics, we would say that the kinetic energy of the block is llost due to the frictional force.
`➢` On examination of the block and the table we would detect a slight increase in their temperatures.
`➢` Thus the work done by friction is this raises the internal energy of the block and the table. In winter, in order to feel warm, we generate heat by vigorously rubbing our palms together.
`➢` We shall see later that the internal energy is associated with the ceaseless, often random, motion of molecules. A quantitative idea of the transfer of heat energy is obtained by noting that `1 kg` of water releases about `42000 J` of energy when it cools by `10 °C`.
`color{red} ► color {blue} bbul" Chemical Energy"`
`➢` As we learnt to rub two flint stones together (mechanical energy), got them to heat up and to ignite a heap of dry leaves (chemical energy), which then provided sustained warmth.
`➢` A matchstick ignites into a bright flame when struck against a specially prepared chemical surface. The lighted matchstick, when applied to a firecracker, results in a spectacular display of sound and light.
`➢` Chemical energy arises from the fact that the molecules participating in the chemical reaction have different binding energies. A stable chemical compound has less energy than the separated parts.
`➢` A chemical reaction is basically a rearrangement of atoms. If the total energy of the reactants is more than the products of the reaction, heat is released and the reaction is said to be an exothermic reaction.
`➢` If the reverse is true, heat is absorbed and the reaction is endothermic. Coal consists of carbon and a kilogram of it when burnt releases `3 xx 10^7 J` of energy.
`color{red}☞` Chemical energy is associated with the forces that give rise to the stability of substances. These forces bind atoms into molecules, molecules into polymeric chains, etc. The chemical energy arising from the combustion of coal, cooking gas, wood and petroleum is indispensable to our daily existence.
`color{red} ► color {blue} bbul " Electrical Energy"`
`➢` The flow of electrical current causes bulbs to glow, fans to rotate and bells to ring. There are laws governing the attraction and repulsion of charges and currents, which we shall learn later. Energy is associated with an electric current. An urban Indian household consumes about 200 J of energy per second on an average.
`color{red} ► color {blue} " The Equivalence of Mass and Energy"`
`➢` Till the end of the nineteenth century, physicists believed that in every physical and chemical process, the mass of an isolated system is conserved. Matter might change its phase, e.g. glacial ice could melt into a gushing stream, but matter is neither created nor destroyed; Albert Einstein (1879-1955) however, showed that mass and energy are equivalent and are related by the relation
`E=mc^2`...............(6.20)
where `c`, the speed of light in vacuum is approximately `3 xx 10^8 m s^(–1)`. Thus, a staggering amount of energy is associated with a mere kilogram of matter
`E= 1 xx (3 xx 10^8)^2J = 9 xx 10^16 J`
`=>` This is equivalent to the annual electrical output of a large `(3000 MW)` power generating station.
`color{red} ► color {blue} bbul " Nuclear Energy"`
`=>` The most destructive weapons made by man, the fission and fusion bombs are manifestations of the above equivalence of mass and energy [Eq. (6.20)].
`➢` In the previous section we have discussed mechanical energy. We have seen that it can be classified into two distinct categories : one based on motion, namely kinetic energy; the other on configuration (position), namely potential energy. Energy comes in many a forms which transform into one another in ways which may not often be clear to us.
`color{red} ► color {blue} bbul" Heat"`
`➢` We have seen that the frictional force is excluded from the category of conservative forces. However, work is associated with the force of friction.
`➢` A block of mass `m` sliding on a rough horizontal surface with speed `v_0` comes to a halt over a distance `x_0`.
`➢` The work done by the force of kinetic friction `f` over `x_0` is `–f x_0`.
`➢` By the work-energy theorem `m v_0^2 //2 = f x_0` . If we confine our scope to mechanics, we would say that the kinetic energy of the block is llost due to the frictional force.
`➢` On examination of the block and the table we would detect a slight increase in their temperatures.
`➢` Thus the work done by friction is this raises the internal energy of the block and the table. In winter, in order to feel warm, we generate heat by vigorously rubbing our palms together.
`➢` We shall see later that the internal energy is associated with the ceaseless, often random, motion of molecules. A quantitative idea of the transfer of heat energy is obtained by noting that `1 kg` of water releases about `42000 J` of energy when it cools by `10 °C`.
`color{red} ► color {blue} bbul" Chemical Energy"`
`➢` As we learnt to rub two flint stones together (mechanical energy), got them to heat up and to ignite a heap of dry leaves (chemical energy), which then provided sustained warmth.
`➢` A matchstick ignites into a bright flame when struck against a specially prepared chemical surface. The lighted matchstick, when applied to a firecracker, results in a spectacular display of sound and light.
`➢` Chemical energy arises from the fact that the molecules participating in the chemical reaction have different binding energies. A stable chemical compound has less energy than the separated parts.
`➢` A chemical reaction is basically a rearrangement of atoms. If the total energy of the reactants is more than the products of the reaction, heat is released and the reaction is said to be an exothermic reaction.
`➢` If the reverse is true, heat is absorbed and the reaction is endothermic. Coal consists of carbon and a kilogram of it when burnt releases `3 xx 10^7 J` of energy.
`color{red}☞` Chemical energy is associated with the forces that give rise to the stability of substances. These forces bind atoms into molecules, molecules into polymeric chains, etc. The chemical energy arising from the combustion of coal, cooking gas, wood and petroleum is indispensable to our daily existence.
`color{red} ► color {blue} bbul " Electrical Energy"`
`➢` The flow of electrical current causes bulbs to glow, fans to rotate and bells to ring. There are laws governing the attraction and repulsion of charges and currents, which we shall learn later. Energy is associated with an electric current. An urban Indian household consumes about 200 J of energy per second on an average.
`color{red} ► color {blue} " The Equivalence of Mass and Energy"`
`➢` Till the end of the nineteenth century, physicists believed that in every physical and chemical process, the mass of an isolated system is conserved. Matter might change its phase, e.g. glacial ice could melt into a gushing stream, but matter is neither created nor destroyed; Albert Einstein (1879-1955) however, showed that mass and energy are equivalent and are related by the relation
`E=mc^2`...............(6.20)
where `c`, the speed of light in vacuum is approximately `3 xx 10^8 m s^(–1)`. Thus, a staggering amount of energy is associated with a mere kilogram of matter
`E= 1 xx (3 xx 10^8)^2J = 9 xx 10^16 J`
`=>` This is equivalent to the annual electrical output of a large `(3000 MW)` power generating station.
`color{red} ► color {blue} bbul " Nuclear Energy"`
`=>` The most destructive weapons made by man, the fission and fusion bombs are manifestations of the above equivalence of mass and energy [Eq. (6.20)].