What Does 8.9876e+3 Joules Mean?

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Discussion Overview

The discussion revolves around the meaning and implications of the energy value of 8.9876e+3 joules, particularly in the context of a human cell's annihilation. Participants explore analogies and comparisons to real-world energy scenarios, including kinetic energy and potential energy from dropping objects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant calculates that a human cell yields 8.9876e+3 joules when annihilated and seeks to understand its real-world significance.
  • Another participant suggests using the Wikipedia page on energy orders of magnitude for context and questions the interpretation of "annihilation" in terms of rest energy versus other processes.
  • A participant notes that the energy value is roughly equivalent to about 2 calories or the energy stored in a AA battery.
  • There is a repeated inquiry about translating the energy value into kinetic energy comparisons.
  • One participant advises approximating the energy to 1e+4 joules for easier calculations and provides examples of potential energy and kinetic energy scenarios that correspond to this value.

Areas of Agreement / Disagreement

Participants express varying interpretations of the energy value and its implications, with no consensus reached on specific analogies or comparisons. The discussion remains open-ended regarding the exact real-world equivalents of 8.9876e+3 joules.

Contextual Notes

Participants mention different methods of calculating energy, such as using E=mc^2 for rest energy and mgh for potential energy, indicating a reliance on various assumptions and definitions that are not fully resolved.

GrayBush
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Hey there, not sure if I am posting this in the right place, so I apologize if I am not.

So after some calculation I came up with an average human cell yielding
8.9876e+3 joules if annihilated.

But what does that figure mean in the real world? I suppose I am looking for an analogy here along with a more refined number. Is it equal to the energy of somebody dropping a brick or a D battery or...
 
Science news on Phys.org
http://en.wikipedia.org/wiki/Orders_of_magnitude_(energy) should give you some idea of what's in the neighborhood. I'm not sure if you mean by "annihilation" that the cell is converted into its rest energy by [itex]E = mc^2[/itex] or some more subtle process.

But really, you should be able to figure out the potential energy changes from dropping objects by [itex]mgh[/itex] also, for a rough estimate. I figure a 100 kg man dropped from a height of 10 meters (about 3 stories) is in the same ballpark as far as the energy goes.

If you really want to blow your mind, though, you can see from wiki that this is only on the order of ~2 calories. Yes, calories from food. Or about the same energy as that stored in a AA battery.
 
Yeah, it was resting energy figured using E=mc^2. Okay, so if translated into kinetic energy what would that (8.9876e+3 joules) be comparable to?
 
GrayBush said:
Yeah, it was resting energy figured using E=mc^2. Okay, so if translated into kinetic energy what would that (8.9876e+3 joules) be comparable to?

Save yourself some grief and decide that if you're looking for "comparable", you'll be OK with +/- 20%... And think about 1e+4 joules instead of 8.9876e+3 joules because it's way less work and won't change the comparables.

Now you can try it in a few standard equations. For example:

Gravity at the surface of the earth: [itex]E=mgh[/itex]: 104J is what happens when you drop a 10kg weight from a height of 100 meters, or a 100kg weight from a height of 10 meters, or a 1000kg weight from a height of one meter.

Kinetic energy: [itex]E=\frac{1}{2}mv^{2}[/itex]: 104J is 200 kg moving at 10m/sec (imagine a horse running into you at full speed), or 2 kg moving at 100m/sec (a cannonball from an 18th century light cannon at long range), or 20 grams moving at 1000m/sec (a modern rifle bullet).
 

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