Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne E = mc^2
Name: Unknown
Status: N/A
Age: N/A
Location: N/A
Country: N/A
Date: Around 1993


Question:
What does e=mc^2 mean?



Replies:
By itself, this equation tells us that, when a quantity "m" of matter is converted to energy, the amount produced is equal to m*c^2, where c is the speed of light. One way this equation can be obtained: when Einstein developed the special theory of relativity, he found it predicted that mass increases with speed. When this is applied to a calculation for the kinetic energy KE of a moving object traveling with speed v, one obtains the result KE = (m - m0)*c^2 where m is the (increased) mass of the object when its speed is v, and m0 is the mass of the object when it is at rest. Thus, an increase in kinetic energy is accompanied by an increase in mass. Furthermore, this suggests that, even when the object is not moving, there is a "rest-mass" energy m0*c^2 associated with it.Then the total energy (kinetic + rest-mass energy) is given by E=mc^2 . It was Einstein's great insight to assert that matter and energy in general are, in essence, equivalent and interchangeable. There was other evidence for such an assertion at that time. An experiment done in 1890 confirmed that radiation exerts a pressure when it hits and is absorbed by an object. Interpreted in the context of relativity, one is led to the conclusion that when an object absorbs electromagnetic radiation of energy E, its mass is increased by E/c^2. Thus, it seems reasonable to assign an equivalent mass to radiation. Since then, the correctness of the E=mc^2 equation, as well as the mass- energy equivalence that underlies it, has been widely confirmed by experiment.

R.C. Winther



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory