Physics gives laws to summarize the investigations and observations of the phenomena occurring in the universe.
- Physical quantities that remain constant with time are called conserved quantities. Example, for a body under external force, the kinetic and potential energy change over time but the total mechanical energy (kinetic + potential) remains constant.
- Conserved quantities can be scalar (Energy) or vector (Total linear momentum and total angular momentum).
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.