Notes On Law of Conservation of Energy and Power - CBSE Class 11 Physics
When satin cloth pieces are rubbed against each other, due to friction, sufficient heat is produced to make the hands feel a rise in temperature. The rise in temperature is due to the rise in internal energy of the body, here, and the satin cloth pieces.   Consider that a body is given a push and is then released. When it comes to rest, all its kinetic energy is lost and a part of this kinetic energy is converted into heat and the remaining is lost in doing work against the friction, to overcome friction. There is a slight rise in the temperature of the surfaces in contact.     Chemical energy is produced when the molecules of the reactants participating in a chemical reaction combine to attain greater stability by forming stable compounds. The burning of any form of fuel is a chemical reaction. Burning is an exothermic chemical reaction, where the chemical energy of the reactants is mainly converted into heat energy, which can later be manifested in other forms. Thus in an exothermic reaction, the energy of the reactants is greater than that of the products. Hence, exothermic reactions like combustion of fuels are indispensable in catering to our daily energy needs.           Electricity is the most convenient form of energy. Electricity is a manifestation of electrical energy and is responsible for running many of the devices in our daily lives such as electric bulbs, fans, motors to pump up underground water, grinders etc.   Till the late 19th century, physicists were of the view that the mass of an isolated system remains constant and it is conserved. They believed that matter can be neither created nor destroyed; it can only change from one form to another.   For example, when water is frozen, it turns to ice; the ice melts to water and when water is heated, it turns to vapour. In all the three forms, the matter of the mass of the system remains the same.   Albert Einstein proposed his famous mass-energy equivalence relation,   , Where c = Speed of light in vacuum.   Thus, according to Einsteinâ€™s mass-energy equivalence relation mass and energy are equivalent to each other. Mass can be converted into energy and vice versa. When a mass, m, is destroyed completely, the equivalent energy, E, is produced. Thus, according to Einsteinâ€™s mass-energy equivalence equation, 1 kilogram of matter can produce a humongous amount of energy .     The Law of Conservation of Energy states that the total energy of an isolated system is always conserved and that energy can only be transformed from one form to another but can be neither created nor destroyed.

#### Summary

When satin cloth pieces are rubbed against each other, due to friction, sufficient heat is produced to make the hands feel a rise in temperature. The rise in temperature is due to the rise in internal energy of the body, here, and the satin cloth pieces.   Consider that a body is given a push and is then released. When it comes to rest, all its kinetic energy is lost and a part of this kinetic energy is converted into heat and the remaining is lost in doing work against the friction, to overcome friction. There is a slight rise in the temperature of the surfaces in contact.     Chemical energy is produced when the molecules of the reactants participating in a chemical reaction combine to attain greater stability by forming stable compounds. The burning of any form of fuel is a chemical reaction. Burning is an exothermic chemical reaction, where the chemical energy of the reactants is mainly converted into heat energy, which can later be manifested in other forms. Thus in an exothermic reaction, the energy of the reactants is greater than that of the products. Hence, exothermic reactions like combustion of fuels are indispensable in catering to our daily energy needs.           Electricity is the most convenient form of energy. Electricity is a manifestation of electrical energy and is responsible for running many of the devices in our daily lives such as electric bulbs, fans, motors to pump up underground water, grinders etc.   Till the late 19th century, physicists were of the view that the mass of an isolated system remains constant and it is conserved. They believed that matter can be neither created nor destroyed; it can only change from one form to another.   For example, when water is frozen, it turns to ice; the ice melts to water and when water is heated, it turns to vapour. In all the three forms, the matter of the mass of the system remains the same.   Albert Einstein proposed his famous mass-energy equivalence relation,   , Where c = Speed of light in vacuum.   Thus, according to Einsteinâ€™s mass-energy equivalence relation mass and energy are equivalent to each other. Mass can be converted into energy and vice versa. When a mass, m, is destroyed completely, the equivalent energy, E, is produced. Thus, according to Einsteinâ€™s mass-energy equivalence equation, 1 kilogram of matter can produce a humongous amount of energy .     The Law of Conservation of Energy states that the total energy of an isolated system is always conserved and that energy can only be transformed from one form to another but can be neither created nor destroyed.

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