Two basic quests in physics. Two principal thrusts in physics are unification and reductionism.
1. Unification. In physics, attempt is made to explain various physical phenomena in terms of just few concepts and laws. We try to see the physical world as manifestation of some universal laws. For example, the same (Newton’s) law of gravitation can be used to describe the motion of a body falling towards the earth, motion of the moon around the earth and motion of planets around the sun. Attempts are being made to unify fundamental forces of nature in the persuit of unification.
2. Reductionism. Another attempt made in physics is to explain a macroscopic system in terms of its microscopic constituents. This persuit is called reductionism. For example, thermodynamics was developed to explain the macroscopic properties such temperature, internal energy, entropy, etc., of the bulk systems. Later on, these properties were explained in terms of molecules in kinetic theory and statistical mechanics.