E=mc²

I received a message from Annie:  Thank you for the posting about equations and I can see the value of making math every day, non-scary conversation, but right now I have to solve E=mc² before test day next week.

The most famous one of them all:  E = mc² or energy = mass x speed of light squared.  The sad thing is that this equation is often used in cartoons to describe smart things that nobody understands when Einstein made our lives easier by saying that energy and mass are the same things.  

• You get different types of Energy (E), but remember that all things have energy.  (Scientists will never say “things”, they say “matter”’ – so anything that has weight and takes up space.  If you can see it or touch it, it is matter.)  When you throw a ball, you convert potential energy (so the energy that is in a “thing” when it is not moving) to kinetic energy (the energy that is in a “thing” when it is moving).  
• Mass (m) is not weight.  Mass is the amount of matter that makes up an object.  (So here is the interesting titbit for your next dinner party:  weight measures the pull of gravity – so mass always stays the same, but weight changes as per the gravitational pull.)  Einstein showed us that matter can also change into energy – they are two different forms of the same thing.  Think of mass as frozen energy that can be converted into the energy of motion.
• Speed of light (c) is roughly 299 792 458 m/second.  Speed of light is constant and simply what we use for conversion – similarly to 2,2 pounds in a kg.  Nothing has to move at the speed of light!

E = mc² has more uses than just in cartoon strips, nuclear bombs and power stations.  Open your iTunes quickly and pick your favourite song.  The longer you listen, the weaker the battery is getting – the phone’s battery is being drained to produce energy in the form of sound waves.  How does it do this?  It converts some of your battery’s mass into energy.  You have just watched a live display of E = mc².

Annie, how about something you can do on labour day at your cook-off?  All you will need is a fire, a metal bar, gloves, a bucket of water and a scale.  Weigh the metal bar.  Put the bar in the fire and wait until it is red hot.  I suggest you get some seriously good gloves before weighing them again.  Now, put the same metal bar in the bucket of cold water and wait until it has cooled down before you weigh it again.  What did you find? What you will find, is that the red-hot bar was heavier than the “normal” bar.  Why?  You added energy to the bar when you heated it.  Congratulations to you, you have just started the first steps in raising a future particle physicist.