Mass Definition and 1000 Threads

Mass is both a property of a physical body and a measure of its resistance to acceleration (rate of change of velocity with respect to time) when a net force is applied. An object's mass also determines the strength of its gravitational attraction to other bodies.
The SI base unit of mass is the kilogram (kg). In physics, mass is not the same as weight, even though mass is often determined by measuring the object's weight using a spring scale, rather than balance scale comparing it directly with known masses. An object on the Moon would weigh less than it does on Earth because of the lower gravity, but it would still have the same mass. This is because weight is a force, while mass is the property that (along with gravity) determines the strength of this force.

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  1. Observer2000

    What determines heaviness of objects in Space?

    Why for gravity some things like planets, stars are heavy enough to have a gravity so they don't fall of the space? When a small object can free fall in space, why a planet has a gravity, and they are considered heavy to what formula?
  2. raspberrypienjoyer

    Friction of a sliding mass on a slope

    Could you please help me with this? I guess move of the mass will be determined with kinetic friction.
  3. C18

    I How is the mass of the Earth or the Sun measured?

    Hello , I read the earth and the sun has a mass and google etc gives a measure . When I go the supermarket and buy 1 kg of bananas , they are weighed on scales . Is science lying about the mass of the earth and the sun ?
  4. I

    Trying to understand the relationships between Forces, Mass and Inertia

    I hope i made clear what i mean and i really hope i can get my answers here Thank you very much for answering already
  5. Brian_D

    Oscillatory motion problem: Bicycle wheel rotation oscillation

    I see this system as essentially a simple pendulum. The mass of the wheel seems irrelevant, because it is distributed uniformly in such a way that it cannot affect the oscillation. The first formula above for rotational inertia is the only one I know for a simple pendulum that includes mass...
  6. gabe99

    Thermodynamics - unknown mass

    The answer should be around 39g. I keep getting around 45g. This is the calculation I tried Any feedback on what I am doing wrong ? Regards!
  7. V

    B e=mc^2 conversion prediction?

    i just watched this: and now im wondering, jsut as when the atom bomb converts mass into energy and we can measure it in force and heat and electromagnetic radiation of various wavelengths, obviously just grams, but of what? what particle would we say is representing the 99% of a proton's...
  8. arivero

    A A very peculiar emergent definition of gravity

    Newtonian gravity is the force law such that for any mass M, the circular orbit of any test particle m at a distance equal to the Compton length of M has the same areal speed, independent of M and m. I wonder, have you seen this sort of definition online in the literature? I guess that...
  9. A

    Prove v<c for particles with m>0 using two identities

    I can't figure out how to prove this using only those two identities? I mean in general, I could prove it easy when using relativistic equations, and showing that if ## v = c##, the denominator becomes 0, and if ## v>c##, the denominator becomes an imaginary number (a negative square root)...
  10. M

    I Is Spacetime a Real Physical Entity or Merely a Conceptual Framework in Physics?

    Given that physics is the study of the physical world, what exactly is spacetime if it is an actual "real world thing", a curved medium or "fabric" guiding the movements of masses, and what is the physics of how this guidance works. As far as I know, space is a vacuum (where not occupied of...
  11. D

    A On the same origin of quantum physics and general relativity

    This pop up on anyone radar? Electron mass different throughout the universe? I don't see how this section could have passed peer review: The masses of electrons, muons, and tau can be explained by the different curvatures of universe, galaxy, and solar system, respectively. I've seen crazy...
  12. U

    I Does the amount of hidden mass remain constant?

    According to the dark matter theories is the total percentage of the dark matter's mass across the Universe remains constant as time passes?
  13. Manish_529

    Tension in a rope hanging between 2 trees

    I know that I can draw an FBD and apply Newton's 2nd law to find the relevant equations. But my question here is why is the mg vector or the weight of the entire rope same at every point on it I mean to say that if the mass of the entire rope is say M then how can a small point on the rope also...
  14. AndrzejB

    B Does Particle System Collapse Depend on Mass, Momentum, or Complexity?

    Does the time to the collapse of a particle system depend mainly on its mass/momentum, or complexity? For example macroscopic object. If system is quite isolated, is no spontaneous collapse even massive or complex systems?
  15. Ignorantsmith12

    I How does the strong force give nucleons most of their mass?

    First, I did read this article on Byrons: https://www.physicsforums.com/insights/a-beginners-guide-to-baryons/. If the answer to my question is in there, I'm sorry, but I missed it somehow. Honestly, much of that article went over my head. Other than that, it's as the TLDR says. I have heard...
  16. K

    I A question about Curved Spaces: Gauss and Riemann (Einstein Gravity in a Nutshell by Zee)

    In p. 84, Zee says “In the new coordinates, M is replaced by M’ = R[-1]MR.” However, I figure out M is replaced by M’ = RMR[-1]. Why is M replaced by M’ = R[-1]MR?
  17. hraghav

    Find the mass of odium for both solid and liquid state

    Mass of honorite initially: 4.51 kg at 261.2 K Additional mass of honorite added: 3.75 kg at 261.2 K total mass of honorite is 4.51 kg + 3.75 kg = 8.26 kg Mass of liquid odium: 14.69 kg at 391.14 K Q melt = m honorite × L honorite Qmelt = 8.26kg × 15500J/kg Qmelt = 128030 J Q cool = (m odium)...
  18. H

    Explain why applying different forces to objects of different masses result in different accelerations

    I don't really get why applying different forces to objects of different masses would result in different accelerations. I read my textbook, and I understand the formula F(net) = m*a, and I think the reason may be because mass is inversely proportional to acceleration ? But this doesn't really...
  19. L

    I How to calculate the mass of gas in a tank?

    Dear community, I have a question comparable to https://www.physicsforums.com/threads/calculating-the-mass-of-air-in-a-pressurised-air-tank.1053707/, but with some additional peculiarities. My setup is: 1) I got a time series of gas pressure and temperature, with a time step of 2 minutes 2) I...
  20. S

    Calculating the Relative COG of Two Masses

    I can calculate the COG with the above formula however P2 is unknown. I need to be able to put P2 into another function which will check that the vector A->COG is parallel to the nominated angle. I cannot seem to work this one out algebraically. Any assistance or guidance would be appreciated.
  21. L

    A Lyman-Series: calculating the nuclear mass of an isotope

    Assuming I have a given wavelength λ of the hydrogen spectrum and I want to calculate the nuclear mass of the isotope, is my approach correct? Rydberg-formula: $$\frac{1}{\lambda} = R_M \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right)$$ with $$R_M = \frac{R_\infty}{1 + \frac{m_e}{M}}$$...
  22. I_Try_Math

    Calculating torque on a pendulum

    Let ##m_{r}=1## kg be the mass of the rod and ##m_{s}=0.5## kg be the mass of the sphere. ## \tau = -rFsin\theta ## ## = -r([m_{r}+m_{s}]g)sin\theta ## ## =-1.3(1.5)(9.8)sin30 ## ## \tau = -9.6 ## My book's answer key disagrees and my initial thoughts are that maybe the mass in my...
  23. I_Try_Math

    What mass must be placed on the cord to keep the pulley from rotating?

    I suppose to keep the pulley from rotating the net torque has to be zero? Let ## F_{r} ## be the force that the 5 kg mass on the ramp exerts on the pulley and ## F_{d} ## be the force exerted straight down by the other mass on the pulley. Let ## r = 0.3 ## m be the outer radius of the pulley...
  24. I

    B The inverse-square law: Gravitational force on two falling marbles

    Imagine making a hole in the ground, about a mile deep, with a large and square diameter. In the middle of the hole, there is a hollow and narrow tube with all air sucked out. Next to one of the walls, so close that it's touching, there is another hollow tube without air inside. Two identical...
  25. R

    I Deriving e=mc^2, how is it possible?

    I was recently very surprised when I had a looked up relativistic kinetic energy. All sources gave the kinetic energy as the difference between total energy and rest energy, in some or other variant of the formula ##E_k=(\gamma−1)mc^2##. I didn't really understand at first. It seemed overly...
  26. Rick16

    I How can the volume of a star be determined?

    Until very recently I thought that according to general relativity masses curve spacetime as a whole, i.e. the complete abstract 4-dimensional spacetime. It came as a complete surprise to me to learn that you can take away the time-component and are left with a curved 3-dimensional space, which...
  27. Quantum55151

    How Do Mass and Weight Differ?

    In the 2nd question, I definitely think it's D, because the force the rock exerts on your toe is equal in magnitude to the normal force the toe exerts on the rock which in turn is equal to the rock's weight, which is related to m by the constant g. In the 1st question, I am not as certain, but I...
  28. B

    I How Does Mass Influence Spacetime Curvature?

    I have read widely about spacetime but not deeply. I am not good with high mathematics. I am aware of and comfortable with the concept: “matter tells spacetime how to curve, and curved spacetime tells matter how to move.” But not much deeper. This is a thought experiment. Is there an equation...
  29. D

    I What would a calculus author have to say on ##\int r^2dm##?

    So I've been searching around for rigorous explanations for things like ##dx## in physics, I'm not looking to fully commit myself to reading the relevant literature at the moment but just want to know what I'll have to do in order to understand. Perhaps I'll make a separate thread about that...
  30. A

    Potential Energy Problem: Pulling a Chain up onto a Table

    So, the first thing that came to mind when I was trying to figure out how to set this up is that it will be a dU problem. After trying to figure out how to set it up to no avail, I took a look at how they solved it in the solutions manual. It's making absolutely no sense to me... They state...
  31. bellum

    How can I identify the molecular fomula, based on an m/z of 350.7897?

    TL;DR Summary: I have the aforementioned m/z and a mass spec graph, my lecturer completely glossed over how to find the molecular formula so I'm stumped. I have a mass spec with 4 peaks and the m/z value, how can I find the molecular formula.
  32. ergospherical

    I What temperature would 1 keV neutrinos have today?

    Suppose there was a 4th generation of neutrino (X, say) with mass m ~ 1 keV. The other three neutrino generations decouple at T ~ 1 MeV and are not heated during ##e^{\pm}## annihilation (whereas the plasma is heated, leading to a bookwork ##T_{\nu}/T_{\gamma}## factor due to conservation of...
  33. hamishmidd

    Finding a formula for displacement of a mass on a spring using v.

    I have tried to answer this using the relevant equations I am provided on my formula sheet, however I get stuck pretty close to the end. I start with 1/2mv^2=1/2kx^2 at the equilibrium position, and kx=mg, x=mg/k. This gets me to v^2=mg^2/k, but I don't know where to go from there. The potential...
  34. R

    B How Much Mass Required to Demonstrate Gravity?

    If one were to demonstrate gravity independent of earth's constant gravity, how could it be done? Assuming this would need to be done in space, what minimum proportions of mass would be required to demonstrate gravitational pull to a human's naked eye?
  35. kirito

    what the relation between the amplitude magnitude and mass at resonance?

    should I be expecting a higher amplitude at resonance for a mass that's heavier to an extent form another where each is attached to a spring vertically , I assumed that's true since the heavier mass will stretch the spring more meaning when moving like a sin or cos wave the amplitude...
  36. Ranku

    I Determining stellar mass independent of its gravity

    What are the independent and accurate ways of determining stellar mass apart from its gravitational effect?
  37. sandeepts

    B Mass defect and electron transition

    According to STR: E=MC^2. When an electron and proton are independent( without influence of any kind of fields, especially electrostatic fields )their rest masses are Me and Mp. When they combine to form Hydrogen atoms they emit photons. So, some energy loss in the form of photons. So, now...
  38. stephen193

    I Where can I find information about this nucleon mass coincidence?

    I can't possibly be the first to notice this numerical coincidence, but my search skills are inadequate to find information about it, and I was hoping others could point me toward papers on the subject. Neutron mass, mN: 939565420.52 (54) Proton mass, mP: 938272088.16 (29)...
  39. M

    B Energy required to bring 1 kg 1000 meter above the surface of the Earth

    How can i calculate the Energy required to bring 1 kg 1000 meter above the surface of the earth ?
  40. Kostik

    A Variation of CMFR mass density ##\rho## along a world line

    Dirac ("GTR" p. 47) makes an interesting observation immediately after obtaining Einstein's field equations with the simple energy-momentum tensor ##T^{\mu\nu}=\rho v^\mu v^\nu##. (##v^\mu## is the four-velocity.) First, the conservation of matter ##\left( \rho v^\mu \sqrt{-g}...
  41. rosedog09

    Drag Forces and Terminal Velocity

    Teacher says Im wrong on both these questions. I have consulted with other teachers and they say im correct. What do you guys think? 3. As mass increases, so does terminal velocity. 5. Fnet = FDrag - Fg ma = FDrag - mg FDrag = 79(8) + 79(10) FDrag = 632 + 790 = 1422 N Teacher Comments 5...
  42. seonjunyoo

    B I wonder about a particle's energy when mass is obtained or lost

    According to Einstein's formula, energy is generated when mass is obtained or lost. What does losing or gaining mass mean for an atom or particle valence? It's simply because of the formula I don't want this kind of answer I want. What does it mean for an atom or particle to lose or gain mass...
  43. mister i

    B Percentage of known energy in the Universe

    It is said that the universe is made up of approximately 4.9% ordinary matter, 26.8% dark matter and 69.3% dark energy. Why isn't ordinary energy included in this "pie"? I suppose it is included within ordinary matter, but could it be calculated what % are particles with mass and what % is pure...
  44. S

    I Can there be slowly-falling accretion disks in black holes?

    Black holes accrete mass around them and it falls gradually up to the even horizon where mass is trapped by the black hole forever. However, the rate of mass falling from the accretion disk to the black hole ranges from being very fast to very long-lived, depending on various conditions...
  45. S

    Relativistic 2 -> 2 scattering with all equal masses

    Stuck on (c), part (i). Any ideas about what is the most elegant way to prove it, maybe using Mandelstam variables since this exercise is supposed to be about them?
  46. P

    A How the mass term of the Hamiltonian for a scalar fields transform?

    The Hamiltonian for a scalar field contains the term $$\int d^3x m^2 \phi(x) \phi(x)$$, does it changs to the following form? $$\int d^3x' {m'}^2 \phi'(x') \phi'(x')=\int d^3x' \gamma^2{m}^2 \phi(x) \phi(x)$$? As it is well known for a scalar field: $$\phi'(x')=\phi(x)$$ .
  47. I_Try_Math

    Vertical Mass Spring System | Analyzing work

    Is there a typo in this question? Supposing there was no friction, the block would fall until the force of the spring was equal to ##mg = 2 * 9.8 = 19.6##, taking the upward y direction as positive. Since ##F_{spring} = -200y## and ##19.6 = -200(-0.098)##, the block would fall 9.8 cm. It's not...
  48. keyzan

    Wave function of infinite potential well

    Hi guys i have this exercise: A particle of mass m, confined in the segment -a/2 < x < a/2 by a one-dimensional infinite potential well, is in a state represented by the wave function: 1. Determine the constant N from the normalization condition. To do this, I have to integral the square...
  49. M

    Why does mass not affect sliding speed down an inclined plane?

    I think that both kids experience the same acceleration (irrespective of mass) since the only force pushing them downwards is acceleration due to gravity, which is the same for both of them. Thus, since they start sliding down the hill at the same time (assumption), and are accelerating at the...
  50. bhobba

    B Is the Higgs Boson the Only Source of Mass?

    This is meant for our younger readers who have only seen popular accounts of where mass comes from. They often say it comes from the Higgs boson, which is sort of true. But it is deeper than that. Sabine has given a deeper popular account in the following video: As an aside, forget this...
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