4 ms·

Energy is a slippery concept. To Wikipedia it's a 'quantitive property' that 'must be transferred to an object.' A property. Good luck weighing that, or nailing

Energy is a slippery concept. To Wikipedia it's a 'quantitive property' that 'must be transferred to an object.' A property. Good luck weighing that, or nailing it to a tree. Consider the 'transformation of energy' ... from mechanical to electrical to acoustical to chemical to potential to kinetic to thermal (end of the line). What is the 'it' that's being transformed? In one sense all things are 'energetic' so long as they have a velocity (relative to something else). We need to keep an eye on boulders up on hillsides. They're not moving right now ... but their potential energy might be transferred to us, thanks to the equally mysterious 'gravity'. Yes, the math all seems to work. But we're not quite 'there' yet. Our position is uncertain.

robomartin 7y ago
Is heat really the end of the line? Heat engine to mechanical, etc.
- TeMPOraL 7y ago
  That's an interesting question. AFAIU, heat engines don't take energy from heat, but from heat difference. In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation, but moving mass between two points of different potential lets you store or extract energy. OTOH, from what little I remember from reaction kinetics in chemistry, temperature there is used as absolute value that determines the chance of collision between their molecules and the "activation energy", both of which influence the rate of a chemical reaction. In this space, thermal energy seems like something absolute. What gives?
  - saagarjha 7y ago
    > In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation Not quite. Potential is defined with an arbitrary basis as you’ve pointed out, but with temperature the basis is not arbitrary: it’s chosen for us, and this value is absolute zero. Taking a temperature difference is not enough to figure out how well a heat engine will work on it.
  - cygx 7y ago
    Note that general relativity requires you to precisely locate all (non-gravitational) energy contributions as they determine spacetime curvature. So while eg the electrostatic potential has an arbitrary zero point, the energy density of the electromagnetic field has not. The only exception to that is gravitational energy, which cannot entirely be localized.
LessDmesg 7y ago
Energy is the ability to perform work. It doesn't have to be a velocity. A boulder on the hillside is energetic because it can fall down, thereby performing work on whatever it falls on.
madhadron 7y ago
Many of the primitive notions that emerge in scientific theories don't correspond to a category like "object I can hold in my hand". Energy is one. Momentum is another. Gene and species in biology. Electronegativity in chemistry. Power dynamic in history. Schema in child psychology. > What is the 'it' that's being transformed? This is exactly what led to the caloric theory of heat. But nonphysical transfer isn't terribly slippery. Take a rumor. I whisper to someone, who whispers to someone...there is no physical transfer here, merely a transfer of configuration. Transfer of energy, like transfer of genes, is more like that. Nor need it correspond to any particular physical part of a thing, e.g., where is the sarcasm in a sentence? Locally conserved invariants like energy or momentum don't correspond to any of the categories that we learn in childhood, but that doesn't make them particularly slippery, just unfamiliar.

robomartin 7y ago

Is heat really the end of the line? Heat engine to mechanical, etc.

TeMPOraL 7y ago
That's an interesting question. AFAIU, heat engines don't take energy from heat, but from heat difference. In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation, but moving mass between two points of different potential lets you store or extract energy. OTOH, from what little I remember from reaction kinetics in chemistry, temperature there is used as absolute value that determines the chance of collision between their molecules and the "activation energy", both of which influence the rate of a chemical reaction. In this space, thermal energy seems like something absolute. What gives?
- saagarjha 7y ago
  > In this sense, heat is like potential energy - an absolute value is arbitrary and meaningless in isolation Not quite. Potential is defined with an arbitrary basis as you’ve pointed out, but with temperature the basis is not arbitrary: it’s chosen for us, and this value is absolute zero. Taking a temperature difference is not enough to figure out how well a heat engine will work on it.
- cygx 7y ago
  Note that general relativity requires you to precisely locate all (non-gravitational) energy contributions as they determine spacetime curvature. So while eg the electrostatic potential has an arbitrary zero point, the energy density of the electromagnetic field has not. The only exception to that is gravitational energy, which cannot entirely be localized.

LessDmesg 7y ago

Energy is the ability to perform work. It doesn't have to be a velocity. A boulder on the hillside is energetic because it can fall down, thereby performing work on whatever it falls on.

madhadron 7y ago

Many of the primitive notions that emerge in scientific theories don't correspond to a category like "object I can hold in my hand". Energy is one. Momentum is another. Gene and species in biology. Electronegativity in chemistry. Power dynamic in history. Schema in child psychology. > What is the 'it' that's being transformed? This is exactly what led to the caloric theory of heat. But nonphysical transfer isn't terribly slippery. Take a rumor. I whisper to someone, who whispers to someone...there is no physical transfer here, merely a transfer of configuration. Transfer of energy, like transfer of genes, is more like that. Nor need it correspond to any particular physical part of a thing, e.g., where is the sarcasm in a sentence? Locally conserved invariants like energy or momentum don't correspond to any of the categories that we learn in childhood, but that doesn't make them particularly slippery, just unfamiliar.