The Sound of Science - "Why Does E=mc2?"

Feb 8, 2019

Jeremy:  Greetings, I’m Jeremy from NIU STEAM.

Sam: And I’m Sam, and this is the Sound of Science on WNIJ.

Jeremy:  Today’s question was asked by Hunang from Orland Park.

Hunang: I'm Hunang, I am from Orland Park and I would like to know, why does E=mc2? 

Sam:  That’s a great question, and one we should be able to answer relatively easily. Get it, relativity?

Jeremy: Good one Sam! Yes, Einstein’s mass-equivalence principal is one of the most simple and elegant laws in physics. It tells us that amount of energy (E) an object has is directly related to its mass (m).  

NIU STEM Outreach

Sam: In this case, the constant c equals the speed of light, which is about 300,000 km/s. So, squaring it gives us a much, much larger number.

Jeremy:  That means if we can change even a tiny fraction of an object’s mass into pure energy, we end up releasing tremendous amounts of energy.

Sam: This is how nuclear power plants work. In a nuclear fission, unstable heavy elements decay to form lighter ones.  When we add up the masses of these new lighter elements, it turns out they don’t weigh quite as much as the original heavier element did.  That tiny bit of missing mass changes into a whole lot of energy.

Jeremy: Scientists are also looking at ways to create nuclear fusion to produce cleaner energy for the future.

Sam: In nuclear fusion, two smaller elements combine to create a heavier element.  The new element while heavier, still weighs just a bit less than the sum of the original elements did.  That extra mass is transformed and given off as energy.

Jeremy:  This is how the stars produce energy.  Our sun combines very light elements like Hydrogen into heavier elements like Helium.  In the process, each individual reaction changes a tiny bit of mass into pure energy.

Sam: Using E=mc2, we can calculate how much energy would be released from a given amount of mass.  But we can also calculate how much an object’s mass would change if we changed its total energy by speeding it up or slowing it down.  As objects approach the speed of light, the energy required to move them that fast actually causes them to increase in weight at the same time.

Jeremy: Woah, that’s heavy, Doc. Keep all those great questions coming to us at stemoutreach@niu.edu.

Sam: This has been the Sound of Science on WNIJ.

Jeremy: Where you learn something new every day.