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32

Yes, photons can. See https://en.wikipedia.org/wiki/Radiation_pressure (and photons are certainly massless). PS In fact, any massless particle has momentum (which has a fixed value since they can only travel at the speed of light) and if it is scattered on a body, it changes its own and the body's momentum, which is what a force does.


17

The most precise measurement of the mass of an electron was reported by Sturm et al in Nature 506, 467–470 (27 February 2014), quoting a relative precision of $3\times 10^{-11}$, meaning they determined the mass to better than $3\times 10^{-41}~\rm{kg}$. If that is not the best, at least it gives you an upper bound... Note that if you could weigh such a ...


5

Newton's 2nd Law of Motion gives the impressed force as $F=dp/dt$, so a physical theory for a massless particle exerting a force requires that the particle have momentum, $p$. First we will discuss mass, momentum, the force law, and Special Relativity. In Newtonian physics mass is identified in two ways: by it's inertia, or as the quantity of matter. The ...


5

Is there another way to conclude the Schwarzschild solution has a mass M It's not so much a conclusion as a definition. From Schutz in "A first course in general relativity", section 8.4 "Newtonian gravitational fields", pages 207 - 208: Any small body, for example a planet, that falls freely in the relativistic source's gravitational field ...


5

This question touches on the distinction between weight and mass which are used confusingly synonymously in many Western everyday-languages (not so in e.g. Russian). Weight is the force of gravity pulling you down. It is proportional to the object's mass which explains the confusing everyday usage of the word. A bathroom scale really measures the force ...


4

Conserved quantities in GR In GR, energy (or mass) is typically an ill-defined concept. In flat spacetime, we define energy as the conserved quantity corresponding to time translational symmetry. Extending this to GR is quite tricky mainly because, what one is calling time is already observer dependent (this is of course also true in flat spacetime, but at ...


4

I want to offer a different perspective from the already existing answers, which all seem to somehow refer to the Standard Model or other specific physical theories to say that mass is not an integral multiple of some fundamental mass unit, hence not discretized. The reason why mass is not like that - and can indeed conceivably have continuous values in a ...


3

See moment of inertia is analogous to mass. Moment of inertia can be thought of as a physical "property" of the object similar to that of mass. And as we know that mass does not depend on any force or gravitational field or any other external effect, so does moment of inertia. Hope this answers your question.


3

Let us for simplicity work in units where the speed of light $c=1$ is equal to one, and assume that there is no cosmological constant $\Lambda=0$. A spherically symmetric vacuum solution to the EFE of the form $$\tag{1} ds^2~=~g_{tt}(r)dt^2 + g_{rr}(r)dr^2 +r^2 d\Omega^2,$$ such that it asymtotically becomes Minkowski space $$\tag{2} ...


3

For Newton's Laws to hold, mass must not vary. Wherever you read otherwise was mistaken. Take a look at this answer. It contains a description of why mass must be constant in Newton's Laws in the context of the rocket equation ... but the analysis applies generally. Newton's Laws are not valid for variable mass systems.


2

Why does a mass attract all the masses around it? Because this is what has been observed . No apples falling up have been observed. Why should't it repel Because no repulsion of masses has been observed up to now. There exist experiments at CERN where the gravitational behavior of antimatter is probed and maybe in the future there will be an ...


2

In general relativity, the field equation relates the metric (through the associated curvature tensor) to the stress energy tensor $T^{\mu\nu}$. This can be interpreted as a flux of energy and momentum in spacetime (i.e. integrating $T^{\mu\nu}$ over a spacetime hypersurface, like a three dimensional hypersurface of constant time, tells you the rate at which ...


2

If the rocket maintains the same rest mass and also the same thrust in the center of mass system, its terminal velocity can be as close to the speed of light as you wish. It will just take forever. It is interesting to ask when a given velocity is reached. Say the thrust remains the same all the time in a stationary frame. The mass of the rocket will grow ...


2

All other things being equal, if a heavier object will roll at a higher speed down hill than a lighter one With the qualification "All other things being equal" your statement is not correct. The falling acceleration is the same because doubling the mass of an object doubles the force causing the acceleration (the object's weight) which means that ...


2

I'm not 100% sure of your level so just as a heads up, I put some comments in parentheses that are meant to give technical caveats. If they don't make sense just ignore everything in parentheses, the zeroth order answer You can look at it that way, but actually it turns out to be much more complicated to understand what's going on in detail. (Basically you ...


2

An example of the sort of system you describe would be the Earth and the Moon, with the Earth playing the part of your mass $m_1$ and the Moon $m_2$. Neither of these are point masses, but courtesy of Gauss' law we know that the gravitational field of a sphere is the same as the gravitational field of a point mass provided you are farther away than the ...


2

The rotation will not necessarily be parallel to the ground. The general motion will be a combination of rotation in a horizontal plane (the conical pendulum) and oscillation in a vertical plane (the simple pendulum). If the support (pivot) is a fixed point, the motion you get depends on the starting conditions. If you launch the mass horizontally at the ...


2

Yes the human body has a gravitational field, and yes it's large enough to be measured experimentally (see the Cavendish experiment).


2

Any time you have an equal and opposite force acting on two bodies, the effect is proportional to $\frac{1}{m}$ for each one. The combined effect is proportional to $$\text{(effect)} = \left( \frac{1}{m_1} + \frac{1}{m_2} \right) \text{(action)}$$ When inverted to find which action has a desired effect we get the reduced mass $$ \text{(action)} = \left( ...


2

I assume you are familiar with Wigner's classification in d=4, as you might be implying. The m→0 limit is best appreciated on the Poincaré sphere, but let us skip that here to count particle states. So, reviewing Wigner, for a massive state, we can Lorentz-transform the momentum to the rest frame, (m,0,0,0) so the little group is SO(3) and its vector rep ...


1

The net force on the string is not F. You are pulling the string forward with force F but I think you are forgetting that the block is pulling the string backwards with a force that is almost equal to F. If the masses of the string and block are m and M then for the whole system (string plus block) F=(M+m)a. The net force on the string is F '=ma=mF/(M+m). ...


1

When you state that the two masses are 'kept at rest' I assume you mean that the pulley is prevented from turning. The load on the pulley is then (M+m)g. [If the pulley is not prevented from turning, then to keep the masses at rest we would have to lift the heavier mass M until it became, effectively, the same weight as the smaller mass. The total load ...


1

Well when there is no answer available, I do not think it hurts to try to come up with one. As far as existence is concerned, Geometry and Topology can exist without physical matter, but not vice versa. In fact, there is so much empty space without matter, but no matter without being in space. Empty space has some Geometry and Topology. However, to ...


1

Many of them are calculated. All the ones that have $u$ or $Da$ as the unit are in atomic mass units, referenced above in the table. They just count up the atoms and add. For bacteria, yeast, and the like it will vary from one specimen to another. Not much precision is quoted and it is likely they use the volume (easy to measure with a photograph) and ...


1

In addition to the already given answears this also might be of interest: When hammer and feather are dropped simultaneously they arrive at the same time, when dropped independently the hammer attracts the planet more than the feather, so you are right, the total time until impact is then smaller for the hammer. If you pick up the hammer and let it fall to ...


1

If you measure a force (weight) for a given acceleration (gravity) in order to determine the mass of an object and you haven't started measuring then the mass is undefined. As soon as you apply an acceleration $a>0$ and you measure corresponding force $F>0$ you can determine the mass. Equations are useful only when they can be used to measure things, ...


1

your mass is independent of gravity (ignoring relativity). in space (or on the moon) your scale would not show what it shows on Earth, so it can't be measuring your mass. a scale measures weight, but sometimes converts to mass via $$ Weight = 9.8 N/kg * Mass$$ (near surface of Earth)


1

Does any object needs force to move? For an object to have a velocity , dx/dt , no force is required, by Newtons fist law: If 'yes', does the matter needs mass to form a force? As the answer to the first part is no, the answer to the second one is no, too. It can just have momentum, since mathematically force is defined as dp/dt. Now in ...


1

If $\rho$ is a generic physical quantity, e.g. mass density in this case, then spherical symmetry is represented in the form of $\rho = \rho(\lvert \vec r\rvert)$ and not $\rho = \rho(\vec r)$ with $\vec r$ being the position vector of the point at which the quantity $\rho$ is being measured.It is assumed that the center of mass of the distribution coincides ...


1

In physics we recognize two different kinds of mass: inertial and gravitational. Inertial mass tells us how much an object resists a change in motion - or how much force is needed to effect an acceleration. Gravitational mass describes how much attraction (due to gravity) an object experiences as a result of gravity. Now despite very careful experiments, ...



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