Sameer and Rameez went to Thirupathi during holidy time. They found more crowd even though they have to wait to see God, in queue. Went the crowd started to move, the place was so hot and temperature does not fall. Every one was sweating and got caught in this congested situation. Why it is hot whenever we are in a crowd?
(i) What is internal energy of a system. Give an expression?

Explanation

Wherever there is crowd, we can feel the hotness of air. This is because in the crowded region, people who are moving may have a chance to collide with each other, and also with the atoms or molecules present in that region due to this collision heat energy is released, which forms as a disturbance and spreads from a particle to particle. Any congested room will have this effect mostly. It's just the Brownian motion of the molecules, based on the kinetic theory of gases.
(i) Internal energy (U) of a system is the energy possessed by the system due to molecular motion and molecular configuration.
The internal kinetic energy `(U_(K))` of the molecule is due to molecular motion and the internal potential energy `(U_(P))` of the molecules is due to molecular configuration. It is expressed as `U=U_(K)+U_(P)`