Mass in special relativity what causes these particles to be termed "massless." However, even massless particles have a relativistic mass, which varies with their observed energy in various frames of reference, The invariant mass is the ratio of four-momentum (the four-dimensional generalization of classical momentum) to four-velocity: and is also the ratio of four-acceleration to four-force when the rest mass is constant. The four-dimensional form of Newton's second law is: The relativistic expressions for "E" and "p" obey the relativistic energy–momentum relation: where the m is the rest mass, or the invariant mass for systems, and "E" is the total energy. The equation is
N. S. Krishnan dialogues and expressed them in his drama and films so that the message came across, but the subject was not offended. He acted in nearly 150 Tamil films and the matinee-duo of N. S. Krishnan and T. A. Madhuram (later his wife) was very popular in his day; he also did roles along with leading stage and cine artists such as T. S. Durairaj, "Pulimootai" Ramasamy, C.S. Pandian and writers such as Udumalai Narayana Kavi and Subbu Armugham and gave a number of hits. He was a talented singer and his hits include "Sivakavi", "Raja Rani", and "Manamagal". Though he