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clarice

(5,504 posts)
Wed Jul 6, 2016, 12:40 PM Jul 2016

Ok brainiacs...someone help me...

In regards to E = MC2... I am trying to find a simple working example to how this theory is used.

I'm going to spin out a very simple scenario

ex: trying to determine the E (energy) contained in a 1 lb steel ball

1. By which yardstick is E determined ? Kilo Watt? Something else?

2. If E = MC2...I imagine that the first thing to determine is the mass of the ball.
Is this determined by weight? By size?...and more importantly...what unit of weight
or size measurement would you use for your calculations? Lbs? Ounces? Kilo grams?

3. C2 (speed of light squared) What unit of speed measurement would you use for your calculation?
MP hour? MP sec? Light years?

4. All of the variables listed would have a great impact on calculating E

ok...all that being said please fill in the blanks below with actual figures for me.

Energy of 1 lb steel ball E____= M______C2_______

10 replies = new reply since forum marked as read
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Ok brainiacs...someone help me... (Original Post) clarice Jul 2016 OP
This is a good explainer sharp_stick Jul 2016 #1
I don't think a steel ball at rest contains any energy. annavictorious Jul 2016 #2
E (9 X 10**16 joules per kg * 0.453592 lbs per kg) = m (.453952 kg) * ... Jim__ Jul 2016 #4
That makes MUCH more sense. Thanks Anna. nt clarice Jul 2016 #9
The title of Einstein's paper helps. longship Jul 2016 #3
Klein-Gordon forever! DetlefK Jul 2016 #6
Well, as I wrote, the simple equation is for a body at rest. longship Jul 2016 #7
Some examples: DetlefK Jul 2016 #5
Thanks to everyone...much clearer. nt clarice Jul 2016 #8
Units of measurement have nothing to do with anything here, bvf Jul 2016 #10

Jim__

(14,045 posts)
4. E (9 X 10**16 joules per kg * 0.453592 lbs per kg) = m (.453952 kg) * ...
Wed Jul 6, 2016, 01:57 PM
Jul 2016

... c**2 (9* 10**16 meters**2 per second**2)

That's what I get from that website.

So from 1kg of matter, any matter, we get 9 x 1016 joules of energy. Writing that out fully we get:
90,000,000,000,000,000 joules

longship

(40,416 posts)
3. The title of Einstein's paper helps.
Wed Jul 6, 2016, 01:37 PM
Jul 2016
Does the Inertia of a Body Depend on its Energy Content?

Which means that the most accurate formulation of the famous equation may be:

m = E/c^2

Not the more familiar algebraic equivalent:

E = mc^2

These apply only to a body at rest.

Nobel laureate Frank Wilczek puts it this way:
can some of a body's mass arise from the energy of the stuff it contains? Right from the start Einstein was thinking about the conceptual foundations of physics, not about the possibility of making bombs or reactors.

The concept of energy is much more central to modern physics than the concept of mass. This shows up in many ways. It is energy, not mass, that is truly conserved. It is energy that appears in our fundamental equations, such as Boltzmann's equation for statistical mechanics, Schrödinger's equation for quantum mechanics, and Einstein's equation for gravity.


(From Wilczek's book, The Lightness of Being: Mass, Ether, and the Unification of Forces, a good read if one has interest in such cutting edge things.)

Concerning units, conventionally one uses SI units in science (traditionally, meters, kilograms, seconds). Particle physicists use a more convenient system of units for them, where c = 1 light-second/sec and E = m, both measured in electron-volts.

longship

(40,416 posts)
7. Well, as I wrote, the simple equation is for a body at rest.
Wed Jul 6, 2016, 02:19 PM
Jul 2016

I'll add that it is not a quantum formulation, which IMHO would just confuse an answer to the OPer's clear questions.

DetlefK

(16,423 posts)
5. Some examples:
Wed Jul 6, 2016, 02:11 PM
Jul 2016

1.

Energy measured in Joule, mass measured in kg, speed measured in m/s. That's the SI-system of units of measurement. (There is also the CGS-system, but I find that wholly confusing even though it's supposed to be simpler.)

Joule = kg * m^2 / s^2




2.

Easy examples to get a grip for E=mc^2 are nuclear processes. (Important note: Fusing atomic cores lighter than iron produces energy. Fusing cores heavier than iron costs energy. Cracking atomic cores lighter than iron costs energy, cracking atomic cores heavier than iron produces energy.)

Let's take for example nuclear fission: The atomic core of Uranium has a certain weight. Then it decays radioactively and splits into several particles. The weight of all the particles summed up is still not the weight of the original Uranium-core. That difference in energy is emitted as kinetic energy and as electromagnetic radiation.
This energy that is set free and converted from mass into something usable, that is what drives nuclear reactors and this is where the output of nuclear explosions comes from.




3.

Example: Let's say you have a capacitor with a capacity of 1 Farad, and you charge it at a voltage of 1000 volt. Then the capacitor stores an energy of E = 1/2 * C * V^2 = 500,000 J

c is 300,000 km/s = 300,000,000 m/s

5*10^5 J = m * (3*10^8 m/s)^2 = m * 9 * 10^16 m^2 / s^2

=> 0.56 * 10^-11 kg = m

So a capacitor storing this much energy will be ~5.6 nano-gramms heavier than an empty capacitor. (A grain of salt is about 1 milli-gramm.)

 

bvf

(6,604 posts)
10. Units of measurement have nothing to do with anything here,
Wed Jul 6, 2016, 10:28 PM
Jul 2016

Last edited Sun Jul 10, 2016, 08:47 PM - Edit history (2)

but an intro to dimensional analysis might be helpful to you.

How fast do your fingernails grow in miles per hour?

Hint: there's an answer, just as there's an answer to the question of how fast you might be driving in furlongs/fortnight.

ETA:

I guess what I'm saying here is that units of measurement are NOT variables.

You can measure your height in centimeters, feet, inches, or what have you. Your confusion seems to stem from thinking that it can be measured in anything but units of length, and your question takes on the quality of that of someone wondering how old s/he is in foot-pounds.

Relieved to see zero recs here.

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