The dumb questions thread

[steve_bank]

Combustion ceases. The box goes to equilibrium. Particulates from combustion settle to the bottom. Convection currents cease and the gases settle based on mass.

Where does the loss of mass show up?

 

[skepticalbip]

Combustion ceases. The box goes to equilibrium. Particulates from combustion settle to the bottom. Convection currents cease and the gases settle based on mass.

Where does the loss of mass show up?

In the difference of mass between the individual oxygen atoms and the atoms in the combustible material and the mass of the molecules of them combined by burning.

Take carbon dioxide as an example: The total mass of one carbon atom and two oxygen atoms is greater than the mass of a carbon dioxide molecule... not by much but there is a mass difference.

ETA:
Surely you accept conservation of energy, don't you? That energy can not be created nor destroyed, only converted to a different form? Well by burning that paper in your box light and heat (energy) was released. Where did it come from?

Answer: That energy came from the 'condensed form of energy', mass. (E=mc²)

 

[Loren Pechtel]

Loren, or anybody,

what if the "scale" was a torsion balance. Could we detect the change in mass then?

Around 1962, I was told that the torsion balance was the most sensitive instrument in existence. More recently, in the age of the electron microscope I've been told that the torsion balance is still the most sensitive instrument. So I'm curious.

Way beyond my knowledge. I believe it's still the most sensitive instrument on Earth but that doesn't mean you can't do better in space.

Combustion ceases. The box goes to equilibrium. Particulates from combustion settle to the bottom. Convection currents cease and the gases settle based on mass.

Where does the loss of mass show up?

The CO₂ and H₂O are bound more tightly than the original O₂ and paper. This makes them lighter.

 

[George S]

Loren, or anybody,

what if the "scale" was a torsion balance. Could we detect the change in mass then?

Around 1962, I was told that the torsion balance was the most sensitive instrument in existence. More recently, in the age of the electron microscope I've been told that the torsion balance is still the most sensitive instrument. So I'm curious.

Way beyond my knowledge. I believe it's still the most sensitive instrument on Earth but that doesn't mean you can't do better in space.

Combustion ceases. The box goes to equilibrium. Particulates from combustion settle to the bottom. Convection currents cease and the gases settle based on mass.

Where does the loss of mass show up?

The CO₂ and H₂O are bound more tightly than the original O₂ and paper. This makes them lighter.

The weight loss is not measurable. The weight loss is the energy (e=mc^2) passing out of the box as photons when the flame burns. If it were a mirror box to contain the photons would yield no weight change from visual light. The heat photons pass through the glass, too. Can a mirror reflect those photons too?

 

[steve_bank]

I had to revie it to be sure.

Photons have energy and momentum but no mass. The enrgy of the photons trace back to the energy in the flame.

We humans are always emitting and absorbing thermal photons. At equilibrium we receive and send the same amount.

As the box heats up a potential difference exists between background, say the room, and the box. As he box goes to equilibrium I would think any energy deficit would be recovered in the process.

What happens if the box is made of a perfect black body material? All photons inside are absorbed. As a BB the box radiates in accordance with the BB wavelength distribution at a given temperature.

 

[skepticalbip]

I had to revie it to be sure.

Photons have energy and momentum but no mass. The enrgy of the photons trace back to the energy in the flame.

And where did the energy in the flame come from if not from the mass (E/c²) decrease when the chemical bonding formed the molecules?

We humans are always emitting and absorbing thermal photons. At equilibrium we receive and send the same amount.

Humans emit more heat into the environment than we absorb from the environment. This heat comes from the chemical conversions of metabolism. Our bodies would become damned cold in the winter otherwise.

As the box heats up a potential difference exists between background, say the room, and the box. As he box goes to equilibrium I would think any energy deficit would be recovered in the process.

I don't understand this. What energy deficit?

What happens if the box is made of a perfect black body material? All photons inside are absorbed. As a BB the box radiates in accordance with the BB wavelength distribution at a given temperature.

I would assume that the energy emitted (that comes from the mass (E/c²) loss in the chemical bonding) would be absorbed by the box which would then be emitted into the environment until it reached equilibrium with the environment.

 

[Wiploc]

Combustion ceases. The box goes to equilibrium. Particulates from combustion settle to the bottom. Convection currents cease and the gases settle based on mass.

Where does the loss of mass show up?

The ashes of the paper don't weigh as much as the paper did. Stuff like that.

The difference is minuscule, but nonetheless real.

I think Google tells me that c squared is 8.98755179 × 10<sup>16

A little bit of light and heat came out of the glass box. If we divide that little bit of radiant energy by 8.98755179 × 1016
that give us amount of weight that is gone from inside the box.

It's a small number. Hard to detect with a scale. But we know it's true because mass is a form of energy, and because energy is conserved.

If energy leaves the box, then there's less energy in the box than there was before. In this case, we generated the departing energy by chemical reactions. So the chemicals we end up with have to weigh less than the chemicals we started with.

We have the same number and kind of atoms that we started with, but the atoms are combined differently, and, as a result, weigh less.

Suppose we start with two atoms, A and B. And suppose we end with one molecule AB plus one photon (which leaves the box). In that case, AB weighs less than A and B.

Everybody's telling you this. I don't understand how you can still be confused about it.</sup>

 

[Jokodo]

Steve, which part of "mass/ energy equivalence" do you not understand? The part where mass and energy are equivalent, perhaps?

 

[Loren Pechtel]

Way beyond my knowledge. I believe it's still the most sensitive instrument on Earth but that doesn't mean you can't do better in space.



The CO₂ and H₂O are bound more tightly than the original O₂ and paper. This makes them lighter.

The weight loss is not measurable. The weight loss is the energy (e=mc^2) passing out of the box as photons when the flame burns. If it were a mirror box to contain the photons would yield no weight change from visual light. The heat photons pass through the glass, too. Can a mirror reflect those photons too?

On Earth it's certainly not. Deep in interstellar space, inside an enclosed volume (so it's not being hit by solar wind or starlight), put something in orbit about the box and measure the orbital period with an atomic clock--I think you're getting into the range where it might be detectable.

 

[steve_bank]

You have a long metal rod. You hit one end with a hammer and force is transmitted down the rod. It can not be instantaneous.

At the atomic-molecular scale how is energy transferred down the rod?

 

[bigfield]

You have a long metal rod. You hit one end with a hammer and force is transmitted down the rod. It can not be instantaneous.

At the atomic-molecular scale how is energy transferred down the rod?

Compression wave.

 

[steve_bank]

You have a long metal rod. You hit one end with a hammer and force is transmitted down the rod. It can not be instantaneous.

At the atomic-molecular scale how is energy transferred down the rod?

Compression wave.

The techical term is longitudinal wave, but that does not explain the physics.

I was wondering how the energy transfer occurs at the atomic scale. I do not know off the top of my head..

 

[DBT]

Compression wave transmitted by kinetic energy as molecules are forced together by the initial impact?

 

[bigfield]

You have a long metal rod. You hit one end with a hammer and force is transmitted down the rod. It can not be instantaneous.

At the atomic-molecular scale how is energy transferred down the rod?

Compression wave.

The techical term is longitudinal wave, but that does not explain the physics.

I was wondering how the energy transfer occurs at the atomic scale. I do not know off the top of my head..

At the atomic scale, atoms don't like to get close to each other due to electrostatic forces (i.e. like charges repel, and atomic nuclei are all positively charged). If you push the atoms in your hammer into the atoms in the metal rod, they will push back against the hammer and against the atoms below them in the rod. This reaction happens over and over again, all the way down the rod. The atoms in the metal move at a finite speed, which is why the energy isn't transmitted instantaneously.

 

[bilby]

The techical term is longitudinal wave, but that does not explain the physics.

I was wondering how the energy transfer occurs at the atomic scale. I do not know off the top of my head..

At the atomic scale, atoms don't like to get close to each other due to electrostatic forces (i.e. like charges repel, and atomic nuclei are all positively charged). If you push the atoms in your hammer into the atoms in the metal rod, they will push back against the hammer and against the atoms below them in the rod. This reaction happens over and over again, all the way down the rod. The atoms in the metal move at a finite speed, which is why the energy isn't transmitted instantaneously.

Yup. It's electromagnetic forces between electrons, mediated by photons. Just like pretty much EVERY phenomenon in everyday life that's not gravity. Radioactivity and nuclear physics are really the only exceptions; Either it's stuff falling towards a massive object (Earth, Moon or Sun), or it's electromagnetic interactions between electrons, mediated by photons.

Gravity is too weak for humans to notice unless it involves one of those three objects; And nucleons tend to be buried under a sea of electrons. So the answer to pretty much every question about pretty much every interaction in our lives is electromagnetic forces between electrons mediated by photons.

 

[steve_bank]

The techical term is longitudinal wave, but that does not explain the physics.

I was wondering how the energy transfer occurs at the atomic scale. I do not know off the top of my head..

At the atomic scale, atoms don't like to get close to each other due to electrostatic forces (i.e. like charges repel, and atomic nuclei are all positively charged). If you push the atoms in your hammer into the atoms in the metal rod, they will push back against the hammer and against the atoms below them in the rod. This reaction happens over and over again, all the way down the rod. The atoms in the metal move at a finite speed, which is why the energy isn't transmitted instantaneously.

That makes sense. I would not have thought of it as charge repulsion.

 

[Derec]

That makes sense. I would not have thought of it as charge repulsion.

It's not really charge repulsion as much as electron degeneracy pressure - a pressure exerted because electrons, being half spin fermions, cannot inhabit identical quantum states.

 

[steve_bank]

That makes sense. I would not have thought of it as charge repulsion.

It's not really charge repulsion as much as electron degeneracy pressure - a pressure exerted because electrons, being half spin fermions, cannot inhabit identical quantum states.

Ok, you probably know more thyan I do.

A metal rod is in equilibrium, atoms are moving around in place. An impulse is inut on ne end.

Dimensionally it is Newtons in and Newtons out. Atoms are held in place by atomic forces. Electrons are charged particles which should have a field. How is force transmitted through an atom?

In a ping pong ball there is an elastic deformation. Does the atom physically deform with an equal and opposite reaction force?

 

[Derec]

That makes sense. I would not have thought of it as charge repulsion.

It's not really charge repulsion as much as electron degeneracy pressure - a pressure exerted because electrons, being half spin fermions, cannot inhabit identical quantum states.

Ok, you probably know more thyan I do.

A metal rod is in equilibrium, atoms are moving around in place. An impulse is inut on ne end.

Dimensionally it is Newtons in and Newtons out. Atoms are held in place by atomic forces. Electrons are charged particles which should have a field. How is force transmitted through an atom?

In a ping pong ball there is an elastic deformation. Does the atom physically deform with an equal and opposite reaction force?

Yes, the atom does physically deform in the sense that the nuclei are closer together during compression and that atoms are cheek by jowl in a metal lattice. But atoms do not have a sharply defined radius or surface like a ping-pong ball would. When the nuclei get closer to each other and repel more, so do nuclei and electrons and they attract each other more. Coulomb forces are therefore a wash. So you need quantum mechanics and the idea of electron degeneracy pressure which is related to the Pauli exclusion principle which says that two electrons (or any other fermions) cannot inhabit the same quantum state.

 

[Angry Floof]

Watching the NASA SpaceX launch earlier and now rewatching some of the live stream. How do they know 100% sure that none of those astronauts have COVID?