Fundamentals of Engineering #4 – Let’s Define Energy

definition of energy

Helium atom
(pic from picstopin.com)

Sweet.  This is where we start to get into the fun and interesting stuff – where the engineering magic happens.  Energy!  Physics is like a riddle or puzzle but energy is behind everything just as we’ve discussed before.  Driving your car, working out, sleeping, all energy transformations and transfers.  Engineering magic also happens with tools too.  Energy and tools baby.

What is Energy?

Everybody knows what energy is right?  Well you do.  Energy is one of those words, for me anyways, that is easy to “get” but technically hard to define or pin down.  Maybe because it exists everywhere?  And I didn’t used to “get” energy either, I guess because it was everywhere you kind of overlook it and take it for granted.  You plug something into the wall and it works.

Now, we get to try and analyze it. If most fancy pants scientists were required to pin down one definition of energy I would guess it would be this:

  • the capacity for doing work.

However, this is not a complete definition.  It doesn’t capture the essence of all it does. Energy can produce other effects which cannot possibly be considered work.



Energy may be crazy but it observes laws

what is energy

3 Examples of Heat Transfer
(pic from greenstarpanels.com)

For example, heat can flow from one object to another without doing work; yet heat is a form of energy, and the process of heat transfer is a process that produces an effect. An improved definition of energy might be that energy is the capacity for producing an effect.  Yes, no?

Energy exists in many forms

Energy is generally classified according to the size and nature of the bodies or particles with which it is associated.  They decided that mechanical energy is the energy associated with large bodies or objects – things that are big enough to see.  Thermal energy is energy associated with molecules.  Chemical energy is energy that arises from the forces that bind the atoms together in a molecule.  Electrical energy is associated with particles that are even smaller than atoms Holmes. (If you missed the earlier post on atoms and such – click here.)

But wait, energy isn’t done yet

There are still even deeper energy classifications that we have to mention.  Mechanical energy, thermal energy, and chemical energy (chemical energy is demonstrated whenever combustion or any other chemical reaction takes place) must also be classified as being either stored energy or energy in transition.

stored energy example

Check it – potential and kinetic energy examples.
(pic from sciencevault.net)

Stored energy can be thought of as energy that is actually contained in or stored in a substance or system.  According to the 1960’s Navy, there are two types of stored energy:  potential energy and kinetic energy.  When energy is stored in a substance or system because of the relative positions of two or more objects or particles, that’s potential energy.  When energy is stored in a substance or system because of the relative velocities (which we talked about here) of two or more objects or particles, that is kinetic energy. Mechanical energy in transition is called work.  Thermal energy in transition is called heat. Conclusion Think we got it now, the definition of energy.  The capacity to do work, sort of.  Also the ability to produce an effect such as heat.  This fundamentals post briefly covered the different forms of energy like thermal, mechanical, and chemical.  The post also tried to relate how kinetic and potential energies play parts in stored energy systems.  Stay tuned for the next post, I believe we keep on going. Yep, to keep on reading, fundamentals of engineering #5 – stored energy and more, click here. Any comments or suggestions?  Topics you’d like to see?



If you think you’ve got a good handle on basic energy definitions, maybe you’d like to try my little 5 question quiz?  Click here to give it a shot.

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