Mass Definition and 1000 Threads

In a spherical distribution of matter - such as with clusters of galaxies - how to calculate how much mass there should be for it to not expand with the expanding universe - in other word, for it to be a bound, static system?

Before boost we have Then using the Lorentz boost: I want to calculate: I tried multiplying the matrices together but I never get the stated answer which should be:

The title is a direct quote of this video by Dr. Becky Smethurst, an astrophysicist specializing in black hole research. This is a mistake, right? Supermassive black holes, for example, don't have tiny radii, compared to stellar mass BHs. Then there's the equation she presents seconds later...

Hi. I remember having learnt in school that if you'd like to verify that bodies of different mass accelerate the same in free fall, but don't have a vacuum available, the bodies should be of same size and shape (e.g. spheres). This made sense to me back then because drag should be the same...

My solution was that the final velocity of the fly is equal to the mass of the elephant divided by the mass of the fly, and then multiplies by the delta in the elephant's velocity. My teacher said it was the wrong answer and that the calculations are presumably pretty long

My teacher gave the above answer as a solution. However, I am not convinced that the proportion is really $$\frac{m_1}{m_1+m2}$$. If m2 << m1the proportion would be really big, right? But intuition tells me that it should be the opposite. Furthermore, if m2 >> m1, then one would expect the...

For a rotating system with mass m this theorem says that if it rotates about an axis distance x from but parallel to the axis through it's natural mass center (CM), then I moment of inertia is $$I=I_{CM}+mx^2$$ My thinking is if one move the axis x distance away from the axis through it's CM...

I tried the square root of ((2)(6.67*10^-11)(3.90E+30))/(5.70E+7) I got 1.55*10^-5 and that is wrong. Maybe I am using the wrong equation but this is the one of professor gave me and I don't know what I am doing wrong :-(

I have a doubt about gravitation. Suppose the mass of the Sun halves in an instant, after how long does the Earth ''notice'' it? That is, does the gravitational force also decrease instantaneously? Instinctively I would say yes, but I don't understand why it should be so. If, for example, we...

Hello. Let's say we have two masses, each moving in 90 percentage of light speed in opposite direction. Then what will be the speed of the one mass according to an observer in the other mass?

I'm trying to wrap my head around the mass vs speed equation of mechanical power. If you double mass, you double power. If you double speed, you quadruple power... Fine, but what does that tell us about the relative importance when things aren't doubled? Let's say boxing Agent 1: has 3%...

Let's assume that there is a closed box, with mass M. There are some random quantum processes inside it, say radioactive decay. Let's assume that we can manipulate the decay from the outside somehow, thus 'putting information' into the box. Can that affect its mass?

hi, I noticed that with higher mass decay width also go higher - but for higgs boson its mass is higher that W and Z boson but its decay width is lower , why?

not asking about neutron stars, where gravity holds neutrons together, rather would the strong force hold individual neutrons together in a solid mass, preventing their decay if one could somehow put them together in a lab?

Hello, was the four-momentum of relativity, Pν, supposed to include all mass and energy contributions from every field i.e. electromagnetic, strong, gravitational... Or is it just the momentum of what was known in Einstein's time?

I believe I know the answer to this question, but it is still very informative to ask: Would iron stellar cores still collapse when they reached some mass without degeneracy (by which I mean, if electrons were not indistinguishable, so did not obey the Pauli exclusion principle on such large...

I converted 3.1eV into J, substituted into E = mc^2. Since the energy is the same, I got the same answer for both: 5.52*10^-36 kg. This doesn't seem quite right- I doubt that a photon and an electron have the same mass. So, when two particles have the same charge, does that mean they have the...

What are the non-gravitational ways of determining mass of galaxies, and how accurate are they?

Let's say that the mass of the objest is suddenly bigger, so when I want to maintain the constant movement, my force must increase as well. But will the velocity have the same magnitude? I think that the velocity will be smaller, so if I want to have the same initial velocity, I must apply an...

We put object on weight ang get a mass. What would that mass be if we put a spring between object and weigt, so that the spring woul shrink to half its original size?

Since these two pillars of science have mass as a common core, are they related, essentially the same or not?

Topography of both the object and the surface. Mass/inertia. Moisture, but that can probably fall under topography. I suppose atmospheric pressure, maybe. Or wind. Magnetism. Any others?

What is the initial acceleration of mass 5M .The pulleys are ideal and the string inextensible. My attempt- 2Mg-T=2Ma (for 2M) T=Ma (for M) Solving we get T=2Mg/3 T-N=5MA (for 5M) N=2MA (for 2M) Solving we get A=2g/21 but the given ans. is 2g/23

Belle II Collaboration, "Measurement of the τ-lepton mass with the Belle~II experiment" arXiv:2305.19116 (May 30, 2023). Combining the uncertainties in quadrature, the newly measured tau quark mass is 1777.09 ± 0.136 MeV/c^2. This is a big improvement over the previous Belle II tau lepton mass...

I am trying to verify Newton II. The setup I am using is, Where ##m_1 = 0.887 kg## is a cart and ##m_2 = 0.02016 kg## is a small hanging mass. There is a force sensor on ##m_1## to measure the force acting on it from the string and the acceleration of the cart. To verify Newton's Second Law...

I want to find the cumulative mass m(r) of a mass disk. I have the mass density in terms of r, it is an exponential function: ρ(r)=ρ0*e^(-r/h) A double integral in polar coordinates should do, but im not sure about the solution I get.

According to this, The heat added to the system is proportional to the mass. Does someone please know how that highlighted statement is so? I think it is because the heat increases the internal energy of a system and internal energy is the sum of the translational, rotational, and vibrational...

What is the value of M_{Pl} used in the Planck (CMB) collaboration's observation papers, such as the one referenced in this link: https://arxiv.org/pdf/1807.06211.pdf. Specifically, I am wondering if it refers to the Planck mass or the reduced Planck mass?

According to Leonard Susskind, i.e. the electron has periodically interactions with the Higgs field condensate, that change the electron alternately to be right-handed an left-handed. At 44:20 in the video he says, that, according to the Dirac theory, the mass of the electron is proportional to...

If a mass is moving it has a wavelength - my question is, is the gravitational field of the mass then modulated accordingly ?

Hi I have come across something confusing in rolling motion. If an object moves with a positive V_cm meaning to the right its angular velocity will be clockwise or negative. The formula is V_cm=wR but for a positive V_cm you get a negative w as it moves clockwise if V_cm is to the right...

why is that the gravitational force proportional to product of masses why not sum of masses or something else .........

Any wave mass term decays, similarly if I want to explain redshift by considering massive photon, how much should be the mass? Is it less than today's upper limit. Solution of wave equation ##□ϕ=0## gives a wave that doesn't disperse over time. But wave solution of the form ##(□+m^2)ϕ=0## has...

HI! I tried to solve this exercise, by assuming that it is an inelastic collision, the planet is spherical, and that the rotation axis is parallel to the z-axis, see the figure attached. (1) before the collision, (2) after the collision.I started by assuming angular momentum conservation, which...

I started by summing the forces and torques to get: - ma = mg-T - I*alpha=Tr I then used a=alpha*r and I=Mr^2 to combine the equations and solved for angular acceleration equals 81.75rad/s^2. Plugging this back into a torque equation I got that the net torque is 1.04Nm. However, the problem...

In a study published in the journal Earth and Planetary Science Letters, researchers say their analysis provides evidence that the oxygen-deprived oceans precipitated two mass extinctions around 259 million and 262 million years ago during the Middle Permian Period. "We are studying the...

Is a particle's mass at minimum when viewed at maximum PEP of the wave form; and is the particle's mass at maximum when viewed at minimum PEP? ( vis e=mc2 )

Is there a correlation between the size of a matter particle (defined as its matter wavelength) and the mass of the particle? With the photon, its wavelength and its energy/mass are inversely correlated. Is it also true of matter particles?

in https://www.physicsforums.com/threads/black-holes-to-explode-due-to-evaporation.1051054/page-2#post-6869765 there was a discussion about where the mass inside a black hole is located. according to general relativity it is located in an infinite small point, which causes spacetime to be...

Dear People, I have a question. I have a rotating tube like a line that has two end and one of them is the center of rotation (like a watch arrow just tube), and inside the tube a mass that is moving towards the center of rotation. So the masses moving along the line aka along the length of the...

I reasoned that at the coin's slowest velocity, the energy it has must just be enough for it to reach the highest potential configuration: when the point mass is directly above the centre of mass of the coin, and its GPE is ##mg(R+r)##. I used this to find the minimum velocity, but I can't think...

https://phys.org/news/2023-03-massive-giant-exoplanet-tess.html It is one of the most massive and densest exoplanets. For comparison, Mo has a density of 10.22 g/cm3 and Ta has a density of 16.6 g/cm3. I would suspect that some of the density is derived from the high compressive pressure of...

Article published at Phys.org - Experiment finds gluon mass in the proton https://phys.org/news/2023-03-gluon-mass-proton.html An interesting diagram accompanies the article. Article in Nature (requires subscription or purchase, but one can read the abstract)...

Improved ATLAS result weighs in on the W boson Same dataset, but better analysis methods and some new results from elsewhere that could be used. Money plot from ATLAS: This makes the CDF measurement an even weirder outlier than it was at the time of publication.

Diagram : I draw a picture of the problem situation and paste it to the right. Attempt : Let me assume that the position of the smaller mass ##m## at a given instant of time ##t## is ##x(t)##. (1) Gravitational potential energy ##\frac{GMm}{x} = \frac{1}{2}mv^2(x)##, where ##v(x)## is the...

Starting to explore quantum mechanics, I read strong nuclear force that binds protons and neutron together in nucleus of atom, gives atom its mass. More binding energy means more mass of atom. Hence the query that, for example there are two magnets having a force F1. And we have the same size...

In the sentence "WIMP-nucleon cross sections of 1.2x10-47cm2 at 1 TeV/c2 WIMPs", there is a relationship between cross section and mass. Is there a general formula that relates the two quantities, in that if there is a certain cross section that means it will be associated with a certain mass?

Mass behaves opposite that of other quantum numbers when combining matter (quarks) and antimatter. Why?

Really perplexed me as the answer provided does not solve for mass ... seemingly wants to use mass as a unit of height? Or perhaps I'm off base ... really just curious if this is even correct or possible? Thanks in advance

Where does the ##m## in ##(3.2)## come from? It doesn’t seem to enter anywhere in Feynman rules for the given diagram