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56

You would have much more mass than 100 kg after the wood was burned. As it turns out, wood is made of cellulose and lignin. Both are cross-linked glucose polymers, so a good approximation of what you would get is given by the chemical reaction of burning glucose: $$\rm C_6H_{12}O_6 + 6O_2 \to 6CO_2 + 6 H_2O$$ This means that 6 oxygen molecules combine with ...


32

The limit in the 2020 Particle Data Group Summary is $m_\gamma < 10^{-18}\mathrm{eV} \approx 10^{-27}m_\text{proton}$, based on a 2007 analysis of the magnetohydrodynamics of the solar wind. The PDG reviews are excellent reading on these kinds of questions.


20

Depends on what your sack manages to capture This was a thing that finally helped kill the phlogiston theory of fire (that burning something means releasing the phlogiston enclosed in it): most things got lighter by burning them, but some got heavier! This could only be explained by having some materials contain negative-mass phlogiston, which pretty much ...


13

Relativistic loss of mass is unmeasurable here, but in principle, you’d lose some tiny fraction of the mass by heat transfer to the surroundings. Whether the smoke would weigh more or less than the wood depends on your definition. Oxygen from the air is combining with carbon in the wood to form carbon dioxide. If this counts as smoke, then the smoke weighs ...


12

The mass that is known to exist within (non-primordial) black holes is much less than that known to exist in stars. Even the biggest supermassive black holes are typically 1-10% of the stellar mass of the galactic bulges they reside in, and more typically 0.5% (e.g. see the M-sigma relation). Only the most massive stars produce "stellar mass" ...


8

A falling body does not have constant acceleration. A body falling toward a planet has an acceleration that is inversely proportional to the square of its distance from the center of the planet, so the acceleration constantly increases as it falls. When a body falls only for a short distance, the distance from the center of the planet changes very little, ...


6

Other answers have focused on the combustion products mass, and the mass of oxygen. I want to cover the other part not in those answers. I'm also keeping it very simple, so.bear in mind this isn't how a Chemistry or Physics graduate would describe it. I'm ignoring truly tiny effects that only get noticed at degree level and higher, and being a bit ...


4

"Could we derive the fact that a falling body has constant acceleration from Galilean relativity and only?" No. However, there's a related fact which is true, which I will explain soon. First, let's define what "Galilean relativity" is. It refers to the fact that the laws of physics are the same for people moving at different velocities. ...


3

No, we cannot. In fact, the claim is not even true. Bodies do not fall with constant acceleration. The gravitational force decreases with the distance squared, so as the body falls its acceleration increases, if only a bit. Plus, there is air friction, etc. If the falling distance is short enough that you can neglect the dependence of the gravitational force ...


3

Greetings from Mikhail Lomonosov from 18th century. In chemistry (and burning is pretty much a chemistry) mass is considered a conserved property. (It is a conserved property outside of the chemistry as well, but chemists have the luxury not to deal with the heat energy used or produced, because it has a negligible mass in chemical reactions.) If you have a ...


3

We already include inertia in that equation, so there’s no need for another term. The mass, m, is a quantification of the inertia of the body, which is why the acceleration that a given force produces is proportional to the mass (which is to say the inertia) of the body being accelerated. Without inertia, any net force would produce an infinite acceleration. ...


2

This is more of a computer science question, but it's also something that I find physics students get confused by quite often and it doesn't seem to be mentioned as often as it should be, so I'm not voting to close it. Basically, you're using the wrong arctan function to plot your results. If you use the right one, everything checks out. The arctan function ...


2

In general relativity, which is the consistent picture relativistic gravity, the gravitating source is not "mass", but rather the stress-energy tensor. This is a two dimensional matrix $T_{ab}$, whose components are: $T_{tt} = $ density of matter $T_{ti} = $ ith component of the 3-momentum density of the matter $T_{ii} = $ pressure felt by ...


2

There is no minimal force to overcome inertia. As you said, because $F=ma$ whatever total force $|F|>0$ will cause an acceleration $|a|>0$, even the smallest force will accelerate the object. How big, given a force $F$, is the acceleration going to be, that depends on the inertial mass $m$. So On Mars, because $m$ is a constant, the same force will ...


2

(a) Yes, provided that no other forces act on the mass. (b) "Is the magnitude of the force on a mass due to a spring equal to one value |𝐹|=𝑘𝑥 ? Yes, the magnitude of the force at a particular instant of time is $kx$ in which $x$ is the extension of the spring at that instant. (c) "Or does the spring push with less force as it is released?" ...


2

From The Evolution of Physics: ... all energy resists change of motion; all energy behaves like matter; a piece of iron weighs more when red-hot than when cool ... In answer to your main question, energy from the chemical bonds is converted to energy in the form of heat, so there won't be a change in the mass of the products of combustion and the result ...


2

There are many good and insightful answers here, but I will just add one thing. As stated, the answer to this question is, of course, emphatically no. But I want to come at it a little more from the angle of what relativity actually tells us. First of all, Galilean relativity is not capable of telling us anything about the acceleration at all, except that ...


1

A force as an external influence or action on an object that causes the object to change velocity, that is, to accelerate relative to an inertial reference frame. Newton’s second-law statement, like Newton’s first–law statement, can be applied only in inertial reference frames (Galilean invariance). Newton's second law states: The acceleration of an object ...


1

Electric charge and mass are not the same thing, although there is a pair of equations in which they look similar, namely Coulomb's Law and Newton's Law of Universal Gravitation: \begin{align} \vec F_E &= \frac{kq_1q_2}{\lVert\vec r\rVert^2}\hat r\\ \vec F_g &= -\frac{GM_1M_2}{\lVert\vec r\rVert^2}\hat r \end{align} Here, $q$ are the electric charges,...


1

A proton has positive charge and positive mass. A proton is attracted by an electron and falls to earth. An electron has a negative charge and positive mass. An electron is repelled by an electron and falls to earth. We know of many things that have negative charge, but nothing that has negative mass. Electric charge creates a much stronger force than ...


1

No it would not, for several reasons. First, the expansion of the universe is manifest only on huge distance scales i.e., the typical distance between galaxies. If you scale it down to human distance scales, it is utterly undetectable. Secondly, it progressively separates objects apart in space but it does not create more atoms inside those objects as it ...


1

$\overline{\Psi} = \Psi^\dagger \gamma^0$ is the definition of $\overline{\Psi}$; this is important because $\Psi^\dagger \Psi$ is not a Lorentz scalar. A change of basis proceeds as usual from elementary linear algebra. Given a COB matrix $N$, spinors transform via $\Psi \mapsto N\Psi$ and matrices via $M \mapsto N M N^{-1}$.


1

An interesting question that deserves an interesting answer! Galilean relativity: the laws of motion are the same in all inertial frames. The trick here is in defining a limited reference frame. Practically speaking within a limited reference frame we cannot determine whether we are moving or staying at rest. For example, two skydivers exit an aircraft at ...


1

according to Newton second law and the gravitation law you obtain $$m\,\ddot R=-\frac {m\,M\,G}{R^2}\tag 1$$ where R is die distance from the earth center to the height $~h~$ of the object. for $~R\mapsto R_0+h(t)~$ where $~R_0~$ is the earth radius. Eq. (1) $$m\,\ddot h=-\frac {m\,M\,G}{(R_0+h)^2}=-\frac {m\,M\,G}{(R_0(1+\frac{h}{R_0}))^2}$$ and with $~\...


1

A consequence of the Heisenberg uncertainty principle is that nothing can ever standstill or not oscillate. Everything has to oscillate. I do not think this is a correct deduction. If one measure momentum there is a limit to the accuracy of measuring position , is all that the HUP says. It is an envelope where measurerements of momentum and position at the ...


1

Inertia is an intrinsic property of matter. The term inertia is used in two different senses. In the directional sense, it means "momentum". Think of it as suddenly stopping while traveling by car. You would move forward. Is there any physical force that makes you move forward, no, there isn't. This is why we don't have a special variable for ...


1

Strictly speaking a scale measures weight and a balance measures mass, but it is common, especially in non-technical English, to refer to a "scale" in either case. Most probably your home device is actually a scale and is somehow measuring the force imparted by whatever you put on the platform due to your local gravity. The function to display the ...


1

All permanent magnets have approximately the same density, the density of iron, because they mostly consist of iron or cobalt. Their maximum magnetization is also about the same, about two tesla (lower for ferrites). The difference between materials of permanent magnets is their coercivity, their ability to keep their magnetization against demagnetizing ...


1

Your implicit assumption is that if A and B are both uncertain, then A+B is uncertain. This is not true. The ground state of an atom is not a state of a definite kinetic energy or a state of a definite potential energy, but it is a state of good energy. Relativistically, it's a state with a definite mass-energy.


1

They have different masses. Since the black hole horizon is order of magnitude $M$ from the center of the black hole (the exact proportionality constant depends on spin, ranging from 1 to 2), and since the "surface gravitational force" at the horizon is proportional to $\frac{M}{r^{2}} = \frac{1}{M}$, this means that the smaller the black hole is, ...


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