- #1
fog37
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- TL;DR Summary
- Concept of energy
Hello Forum,
Energy, like space and time, is a common concept but little understood. I think Feynman himself stated energy is hard to describe...
I have a few observations in regards to energy and I would like your feedback on them:
Energy is measured indirectly. Can we measure the energy of a system or can we really measure only energy differences? There seems to be no problem measuring the ##KE## of a system. What about ##PE##? Can we measure ##PE## or just its changes?
Thanks!
Energy, like space and time, is a common concept but little understood. I think Feynman himself stated energy is hard to describe...
I have a few observations in regards to energy and I would like your feedback on them:
- While force, which represents an interaction between two different systems, causes the change in one of the system's configuration and/or state of motion, energy measures the change in the system's configuration and/or state of motion. What does it mean that a system has a certain energy? I think it means that it has the potentiality of changing its own configuration or the configuration/state of motion of another system. Somehow, the textbook definition of energy as the ability of doing mechanical work is deemed incorrect and flawed. Why so?
- All forms of energy seem to boil down, macroscopically and microscopically, to two fundamental energy forms: kinetic energy ##KE## and potential energy ##PE# (I guess radiation would be the 3rd energy type). For example, besides the bulk, organized, macroscopic kinetic energy of a moving body, thermal energy represents the internal and disorganized kinetic energy of the body's microscopic constituents. Chemical energy is the potential energy between molecules and atoms. Nuclear energy is the energy deriving from the particles inside the nuclei.
- As far as potential energy ##PE## goes, the most common ##PE## forms are gravitational potential energy ##PE_g## and elastic potential energy ##PE_{elastic}##. Both ##PE## forms involve two or more entities interacting among each other (PE only makes sense for a system of object).
- After relativity, we learned that mass and energy are intimately related. A point particle has rest mass+##KE## while a composite system has rest mass+##KE+PE##.
Energy is measured indirectly. Can we measure the energy of a system or can we really measure only energy differences? There seems to be no problem measuring the ##KE## of a system. What about ##PE##? Can we measure ##PE## or just its changes?
Thanks!