You are here:

Relativity/nuclear binding energy


Please tell me in detail why energy is released when two nucleon combined with each other. In your answer please give reference of mass defect, strong nuclear force, electrostatic force, etc.

ANSWER: The simple answer is that there is a mass defect realized at the time of combination, because of the strong force attraction. Then conservation of energy requires that the excess energy be emitted.

Perhaps I don't understand what you need.

If two balls of mud collide and merge into one, there is a loss of kinetic energy. The lost kinetic energy is converted into thermal energy and is radiated away.  This is completely analogous to the merger of two nucleons.


---------- FOLLOW-UP ----------

QUESTION: When two clay ball collide then there ke changes to thermal energy but there mass is not reduced. Why this does not happen when two nuclion combine. I mean to say why mass converts to energy? Why energy comes out? Who put this energy? Why not just strong force combine them and stay quite? Why this not happen between electron and proton attraction? I am confused. Please help me out....

When the mud balls collide, their total energy does not decrease, but as the warmth decays by radiation, the total energy of the two-ball system does decrease, and according to the Special Theory of Relativity, their mass must decrease by dE/c-squared. This is a tiny amount, too small to measure in this case.

But the strong force is very strong.  When it makes two nucleons fuse, the fractional change of energy and mass is much larger.  That is why nuclear bombs are very explosive.

The loss of mass between separated particles and a nucleus made from those particles was noticed  early in the twentieth century and was the source of the idea of nuclear weapons.

I cannot explain in simple terms why energy and mass go together, but it follows from the assumptions of Special Relativity (SR).  You would have to study this theory to see where the relation comes from.

Physics theories are not always easy to understand in everyday terms, but SR has been verified by experiments, such as the atomic bombs I mentioned, but also in many other ways.



All Answers

Answers by Expert:

Ask Experts


Uncle Ben


I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.


I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

I have dozens of papers published in the Physical Review and in the American Journal of Physics.

I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.

©2017 All rights reserved.