Recently for one of my college classes I’ve had to do a light recap of basic physics phenomena l. In classic fashion, when being taught a simple concept (like mechanical advantage) I immediately conceptualize a method to mentally torture myself and ask “how does that work exactly? Meaning? what is the essence of mechanical advantage?” This kinda lead me into a rabbit hole where I (I don’t know if this is a correct conclusion, but…) discovered that energy isn’t really a thing, but rather just a concept to describe how things happen. In this note, the very important concept that energy cannot be created nor destroyed is also based on the major assumption that since we can do an experiment with the same outcome tomorrow as we do today, there isn’t inherently more energy being involved and therefore energy must remain consistent.
I was hoping I could unpack this a bit. What really is energy? If my conclusion (again, could very well be wrong) is true and energy isn’t really a “thing,” then how come we have so many formulas that can calculate how much energy a thing has, and why do they work so good at making things?
It is simply the capacity to do work (in the sense used in physics not the common understanding). There are two types, potential and kinetic. A rock sitting on top of a hill has potential energy (weight x height), which gets converted to kinetic energy (1/2 m v**2) when rolling down the hill, assuming no losses to friction. So yes lots of formulas make use of the concept. The law of the conservation of energy applies if you are not talking about atom bombs.
Way back in high school physics when we were first introduced to the concept of “work” the teacher used the example of walking down the hallway carrying a briefcase results in no work being done (motion is at right angle to force). We argued that carrying a briefcase was work as you get tired doing it.
The example was the work done on carrying, not lifting, the briefcase. I think the point was to just get the common definition of “work” out of our thinking.
Energy is the measurable substance of all things/actions physical/measurable. All physical/measurable things/actions are forms of energy. Energy erases the distinction between things and action. Both the things themselves and their motions are forms of energy.
Is their any truth to saying “energy is not a thing?” Sure. Things are forms of energy. So you can say energy by itself is not a thing. But this is only when we restrict ourselves to physical reality. For otherwise we might suppose that energy itself is the measurable/quantifiable form of something more basic. In that case, saying energy is not a thing is no more true than saying water is not a thing just because water has different forms: ice, liquid, and steam.
Well, yes I was familiar with this definition, but I mean what is IT. Like, matter is the stuff that you and I are made of (star dust) so it’s pretty easy to understand. But matter can be turned into energy (via fusion or combustion) and energy into matter (via special creation?). I guess it’s hard to put into words but if I had a jar of energy sitting in front of me, what would I see in the jar?
Mathematical bookkeeping.
An accident, not a substance.
Possibly a way to understand act and potency.
A measure of a things causal powers.
A property of something
Take your pick.
What energy is not is some ethereal substance floating out there in the void—some magical pure energy devoid of a physical medium.
It would look like photons, swirling gases or a compressed spring. You see the physical carriers of energy. But you will never see a jar of pure energy any more than you will see a jar of pure speed or pure tallness. I think you’ve misunderstood the whole energy and mass conversion formula (e =mc^2). This is not one pure substance turning into another substance like currency. For example, missing mass in nuclear processes is found in the form of photons. Physical particles with mass turn into physical particles without mass. Mass and energy are just two fundamentally intertwined properties of a physical system. Mass itself is just another property of things as is energy.
This is for mechanical work done on the briefcase. Obviously the body is doing internal work (you burn calories just maintaining muscle contraction). In order to lift the briefcase it is not difficult to see that work needs to be done against gravity. But once lifted, even a small amount of work is needed to achieve a constant horizontal velocity (from rest). This is an acceleration, however small, and requires a net force applied over some small time and displacement. And this model assumes a perfectly rigid briefcase being carried in a vacuum chamber on roller skates.
The briefcase is certainly not perfectly rigid and encounters air resistance. So there will be small horizontal frictional forces the hand must combat. The work done is negligible. Saying no work is done might be misleading. A walking human also bobs up and down as our center of gravity changes which means your hand is alternating doing positive and negative work on the briefcase. This is far more substantial than the work done against air resistance. Overly pedantic maybe, but I like to make sure my physics students understand the idealized conditions we are working with.
Exactly. We walk by falling forward, which we set up by gaining elevation with each step. There is also friction to consider, unless we are sliding on ice. Curling stones and some people I know avoid work as much as possible.
You seem to be dealing with a basic understanding of matter and what it means to be a ‘thing’. The essential components of the universe are space and matter. Matter consists of everything that possesses mass and/or energy. Energy is the kinetic part of matter while mass is an object of substance with potential energy as described by Einstein’s equation that is used to produce nuclear power. You seem to think that a ‘thing’ must only be an object of substance that has significant mass. Energy is a created thing along with mass and space. An epistemic interpretation of Genesis says, ‘In the beginning God created space and matter, and the matter was without form and void. And darkness was on the face of the deep. And the Spirit of God was moving over the fluid matter’. Basic manifestations of the kinetic energy part of matter are heat, light, and motion. Those are things.
@Vinnie kinda pointed me in a good direction by pointing out that energy is more so a property of matter than a thing (kinda like length or color), so this definitely helps me understand that more. Thanks!
