Revision Notes on Physical World

• Science is a systematic attempt to understand natural phenomena in as much detail and depth as possible, and use the knowledge so gained to predict, modify and control phenomena, and also experimenting and predicting from what we see around us.

• Physics deals with the study of the basic laws of nature and their manifestation in different phenomena. The basic laws of physics are universal and apply in widely different contexts and conditions.

Principle thrusts of Physics:

1. Unification – Attempt to unify fundamental forces of nature as a single set of mathematical relationships.

2. Reduction – Derivation of properties of a bigger, more complex, system from the properties and interactions of its constituent simpler parts.

• Interplay of theory and observation leads to progress in science.

  • As observations become more precise or yield new result, theory must be modified to account for them.

  • Theoretical advancements suggest what to look for in some experiments and thus design them accordingly.

• There are two domains of Physics- macroscopic and microscopic.

  • Macroscopic domain deals with phenomenon at laboratory, terrestrial and astronomical scales.

  • Microscopic domain includes atomic, molecular and nuclear phenomenon.

• Physics gives rise to new technology and subsequently new technology helps developing new laws of physics based on state of the art equipments in experiments.

• All the forces present in universe can be categorized in four 'Fundamental Forces' namely -

  • Strong Nuclear Force- It is the force that is exerted among nucleons(protons and neutrons) and keeps the nucleons bound inside nucleus despite of electrostatic repulsion. Its magnitude is independent of the charge of the particle. This is the strongest fundamental force. Its range is extremely small(~10^-15 m).

  • Electrostatic Force- It is the force exerted between charged particles. Quantitatively this force is expressed by Coulomb's law.  It is weaker than Strong Nuclear Force but stronger than the other two. This force is repulsive between like charges and attractive between unlike charges. Tension, friction, normal force, and dynamics of chemical reactions have electrostatic force underlying them.

  • Weak Nuclear Force- It appears only in certain nuclear processes like β-decay of nucleus. Its range is 10^-16 m.

  • Gravitational Force- It is the force of mutual attraction between any two objects by virtue of their masses. It is the weakest of the four fundamental forces but has the largest range. It keeps the celestial bodies revolving in their orbits.

• Efforts of physicists lie in unifying all theories in all domains into one. Electric and magnetic phenomenon have been unified into electromagnetism. Electromagnetic and weak nuclear force have now been unified as electro-weak force.

• Physicists attempt to discover laws that summarize the reasons behind physical phenomena. These laws must be independent of position and time of where the experiment is conducted.

• In a physical phenomenon involving different force, the quantities that do not change with time are called 'conserved quantities'. Those are expressed as laws. For example, law of conservation of energy, law of conservation of linear momentum, law of conservation of angular momentum, parity, etc. These laws have deep connection with symmetries in nature.