Scivillage.com Casual Discussion Science Forum

Richard Feynman once wrote: "It is important to realize that in physics today, we have no knowledge what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way."

Which brings me to the "what" that energy should be thought of as being. Now many well-educated physicist enthusiasts tell me it is not a "substance" or "stuff" that can be divided into particles like matter can. And yet we are told at the same time that photons and electrons are irreducible particles themselves, the sums of which compose light and electricity. It seems to me to imply therefore that at least in this case energy IS some kind of stuff if it can indeed be made up of particles and waves as well. In the other case, that of heat, we have energy NOT as a stuff in itself but as the vibrating motion of molecules. So is it a kinetic property like motion or vibration, or is it a stuff like light and electricity? Perhaps both at the same time? And neither! More quantum weirdness no doubt!

Energy includes things like electricity and electron volts, but it also includes mechanical work. So as an encompassing term, it would be hard to have a single, unifying unit of energy. There are just different contexts in which we could quantify a potential for work.

Energy, being essentially fluid and continuous, cannot be quantitatively measured. You can only measure the sum of countable standardized "units"--a mere mathematical abstraction of an agreed upon "amount" and not energy itself. There is no sum "quantity" of energy. There are only lesser and greater intensities of it--higher and lower magnitudes or degrees of power based on qualitative properties and not on measurable units.

Under the (almost) universally agreed units .. SI (System International) .. along the lines of ..

Distance is measured in meters .. a fundamental unit - you just have to accept the definition.
Time is measured in seconds .. another fundamental unit - you just have to accept the definition.

Velocity is meters per second (m/s)
Acceleration is rate of change of velocity m/s/s

Mass is measured in kilograms .. a fundamental unit - you just have to accept the definition

Force is mass * acceleration (kg.m/s/s) conveniently called a Newton (N). 1 Newton is one kg accelerated by 1 meter per second every second.

Work is force * distance. (N.m) or kg.m^2/s/s or kg.m^2/s^2 and is commonly measured in Joules (J)

Power is rate of doing work .. usually Watts (W) so N.m/s
or kg.m^2/s^3

Energy is the ability to do work also measured in Joules.

If you were electrically minded you'd need the Coulomb [or possibly Amp see later] which is the charge on about 6.24 x 10^18 electrons .. to reduce the time spent counting the definition is based on effect rather than actual quantity.

Why did I ever need to know?

Quote:Dimensional analysis is the use of a set of units to establish the form of an equation, or more often, to check that the answer to a calculation as a guard against many simple errors.

https://isaacscience.org/concepts/cp_dim_analysis

If you've got this far you'll see the SI uses Amps not Coulombs and you need Kelvin for temperature but I'm not going back to change anything.

For even more exciting things see:
https://en.wikipedia.org/wiki/Internatio...m_of_Units