# Questions tagged [mass]

The property of an object that determines how much it responds to a force in Newtonian mechanics, and how much it interacts with gravity in the Newtonian framework. Mass also refers to the intrinsic energy of a particle in particle physics.

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### Would equal balance at same height when hung on a balance?

This is based on a question from the gravitation course on Brilliant. As you can see in the diagram below, we have 2 weights hung on a pulley. It is given that: Neither one accelerates when you let ...
1answer
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### Are Instantons Massless?

That is, are the only field configurations which give a non-zero winding number ones in which the Fourier transform includes a factor like $\theta(k^0)\hat{D}\delta(k^2)$, where $\hat{D}$ is some ...
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### How we can prove that photons have no mass? [duplicate]

I am thinking nowadays that how its possible that a particle without mass, actually exists? in the case of light its used to say that photons have no mass no weight but they have momentum. can any ...
0answers
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### If inertial mass changed as a gravitational field changed would we definitely realise

It strikes me that matter can only directly interact with another bit of matter when its in an identical gravitational field. This makes me wonder whether if inertial mass increased and decreased with ...
1answer
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### Meaning of $M$ in Schwarzschild metric

In the Schwarzschild metric $$ds^2 = - \left(1-\frac{2M}{r} \right) dt^2 + \frac{dr^2}{1-\frac{2M}{r} }+ r^2 d\Omega^2.$$ Is it safe to call $M$ the mass of the source of curvature? Or should I ...
6answers
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### Springs with some finite mass

Let us consider a spring which is having some finite mass. By the help of some external agent the spring has been extended by some distance $x$. Will the restoring force produced in the spring still ...
1answer
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### Why is gravity the weakest force if, theoretically, it is made up of all the other forces' fields?

I'm quite new to the physics world and want to get an idea as to how physicists have been able to sum all fields/forces (higgs boson, electromagnetic, weak force, strong force etc) in a said object, ...
2answers
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### Is this relativistic mass?

I have seen in a lot of places in here clearly stating that relativistic mass is outdated, that we can make do just fine with the concept of invariant mass,etc. But I've also seen people saying that a ...
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### Are energy and mass two forms of the same thing?

I know that energy can convert to mass and vice versa. So are we not looking at simply two forms of the same thing?
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### Change of entropy of mixing in terms mass ratio

I am stuck on this problem. Suppose we are mixing substances $a$ and $b$, we have $$\Delta S_{mixing} = -Rn_a \ln (\frac{n_a}{n_a + n_b})-Rn_b \ln (\frac{n_b}{n_a + n_b})$$ and we are told to ...
4answers
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### Why does four-momentum have to be tangent to the worldine?

In relativity, we define momentum for a particle as a vector that is always tangent to the particle's worldline. I am wondering what is the exact reason this is necessary. For a massive particle of ...
2answers
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### If a black hole is created from light, can this black hole then move at the speed of light?

Imagine we managed to squeeze light into a very tiny region of space so that the energy concentration at that point becomes a black hole. Can this black hole then move at the speed of light?
3answers
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### Why do we say that a photon is a particle if it is massless?

If light is made of photon particles and the photon doesn't have any mass but it is a form of energy (according to my thinking) then why do we call photons particles?
2answers
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### Force and center of mass acceleration

https://i.stack.imgur.com/3w7Mt.png I have a rod with mass $m$. Above are two ways I can apply a perpendicular force to the rod. Since the mass of the rod is uniform, its center of mass is in the ...
1answer
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### How much force is needed to move a 70kg person?

I have a science question to answer, and just need some things cleared up. The question states: 'If a sprinter starts out of the blocks and speeds up to reach a top speed of 15m/s in 5 seconds, what ...
6answers
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### If an object with more mass experiences a greater gravitational force, why don't more massive objects fall faster? [duplicate]

According to Sir Isaac Newton, the gravity equation runs like this: $$F = \frac{Gm_1m_2}{r^2}$$ where $F$ is the gravitational force, $G$ the gravitational constant, $m_1$ and $m_2$ are the ...
3answers
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### Does the expansion of the universe explain why the universe doesn't collapse?

Notes: 1. I'm in 8th grade so i don't have in-depth schooling on this. Lengthier explanations with more extra information that would improve understanding would be much appreciated. 2. I asked a ...
0answers
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### QCD Trace Anomaly and Mass

In the paper in equations 4 and 5, some of the mass of the nucleons comes from the "trace anomaly" of the QCD energy-momentum tensor (as described in the paragraph following these equations). Is there ...
1answer
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### Hawking radiation and mass annihilation [duplicate]

Now, i just heard that the particle anti particle pairs that zip in and out of existence every planck second both have positive mass. if that is so, how does hawking radiation work? black holes lose ...
1answer
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### Why does mass cause resistance to acceleration?

If I were in a vacuum with no gravity or friction, why would it be harder to push a floating bowling ball than a marble? Is there anything happening on an subatomic level that makes matter act ...
0answers
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### Why do we believe local gauge invariance (that tells us photons are exactly massless)? [duplicate]

There are experimental upper limits on the photon's mass, but they are finite. I heard that the reason we know that photons have exactly zero rest mass (and thus travel exactly at the universal ...
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### How similarly are light and matter affected by gravity?

For a path of travel in a shape that is straight before it curves, if the curvature of the path is attributable to gravitational force, what additional information (if any) would be capable of ...
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### Can we create negative mass this way? [closed]

First,sorry for the clickbate(kinda). I don't know if this will work or not but It seems worth a shot unfortunately I am stuck on the approach of proving it can't be done.....'cause ofcourse it can'...
2answers
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### Ought we say 'body mass', rather than 'body weight'?

I'm asking in the context of medicine, where you're "massed" (or is it "weighted"?) on a scale. This answer beneath insinuates that 'mass' may be the preferred term, but it doesn't outwardly clarify ...
0answers
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### Can we measure renormalized mass in QFT? [duplicate]

Due to QFT books, we measure pole mass(physical mass) in experiments. From the Lagrangian point of view, renormalized mass is a parameter(in MS bar or some similar renormalization scheme that has an ...
1answer
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### Which is more important for a force of the impact mass or velocity? [duplicate]

If a 2 times bigger mass collides with an object in which a 2 times smaller mass collides but with 2 times the speed which one will produce more force on the object? The object is stationary before ...
3answers
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### How do leptons differ from one another?

All the leptons that I have come across have their native (matter) charges of -1 relative to the charge of an electron. Since they are all fundamental and are not made up of quarks, you can't ...
1answer
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### Gravitation inside spherical hole in universe

I was doing a little thought experiment and ran into a paradox. How to compute the gravitational field inside a spherical hole in a universe that is otherwise filled with uniformly distributed mass? ...
1answer
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### How does one interpret the external force in the equation of motion for a variable mass system?

My question is heavily related to the answer to the question in this link: Second law of Newton for variable mass systems. Answer: https://physics.stackexchange.com/a/142773/223936 I would like to ...
2answers
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### Has the kilogram changed?

In late 2018 the kilogram's definition switched from a physical object (the International Prototype Kilogram) to Planck's Constant; a grand move in my opinion. However, I haven't heard of the ...
4answers
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### Difference between Mass Number and atomic mass unit (AMU)

I am struggling to understand the difference between Mass Number and atomic mass unit (AMU). I read several posts on this site but still confused. Mass Number seems like a number (i.e. number of ...
2answers
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### Mass attached to another mass hanging from a hole in a table

I've been trying to understand the setup for the Lagrangian for this question from Morin: My issue is why would the mass ever rotate, assuming we release it from rest? Why does the setup of the ...
1answer
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### Would a massive graviton emit more massive gravitons?

In the theory of massive gravity, suppose that two bodies start interacting by exchanging gravitons. Wouldn't these gravitons, having mass, have to exchange gravitons between themselves, with these ...
1answer
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### Inertia of a falling weight

I use a standard device (penetrometer) that uses a 10 kg weight that is dropped a constant distance to cause a probe to penetrate soil. The penetration distance after 4 blows is recorded. If I were to ...