Class 11 Physics Physical World Conservation Laws

Conservation Laws

A conservation law is a hypothesis based on observation and experiments which cannot be proved. These can be verified via experiments.

Law of conservation of Energy

• According to the general Law of conservation of energy, the energies remain constant over time and convert from one form to another.
• The law of conservation of energy applies to the whole universe and it is believed that the total energy of the universe remains unchanged.
• Under identical conditions, the nature produces symmetric results at different time. Law of conservation of Mass

This is a principle used in analysis of chemical reactions.

• A chemical reaction is basically a rearrangement of atoms among different molecules.
• If the total binding energy of the reacting molecules is less than the total binding energy of the product molecules, the difference appears as heat and the reaction is exothermic.
• The opposite is true for energy absorbing (endothermic) reactions.
• Since the atoms are merely rearranged but not destroyed, the total mass of the reactants is the same as the total mass of the products in a chemical reaction.
• Mass is related to energy through Einstein theory,

E = mc2, c – speed of light in vacuum

Law of conservation of linear momentum

• Symmetry of laws of nature with respect to translation in space is termed as law of conservation of linear momentum.
• Example law of gravitation is same on earth and moon even if the acceleration due to gravity at moon is 1/6th than that at earth.

Law of conservation of angular momentum

• Isotropy of space (no intrinsically preferred direction in space) underlies the law of conservation of angular momentum.

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