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. S

    Mass of vapor per hour for heating water

    I thought about using Black principle to solve this question but I am confused about the final temperature of system Q released by vapor = Q absorbed by water mvapor . cvapor . ΔTvapor + mvapor.Lv + mvapor . cwater . ΔT2 = mwater . cwater . ΔTwater But what is the final temperature of the...
  2. patrykh18

    Centre of Mass of a Uniform Cuboid -- Show that it is at the Center

    So, I volunteered to run a seminar to first year students in my college. They got a question like this for homework recently and a lot of them made a mistake in the calculation. I am not asking for help with the question itself because I know how to do it. However, a lot of students made a...
  3. F

    I Heaviest particle detected so far

    I'm reading this article on Dark Matter and at some point the authors say '' if the LKP [Lightest Kalusa-Klein Particle] is to account for the observed quantity of dark matter, its mass [...] should lie in the range of 400 to 1200 GeV, well above any current experimental constraint.'' My...
  4. T

    B Reduced mass to atomic mass units conversion help please

    Hello I am trying to understand how to write the reduced mass into atomic mass units but i am confused how it was done. The equation is $$m_1m_2/(m_1+m_2)$$ For two similar masses in my particular case i have: $$m^2 / 2m = 1/2 * m$$ Then to convert to atomic mass units, the book says it...
  5. T

    I Is it possible to extend Newtonian gravity to include energy as well as mass?

    Hello there.My question is:can Newtonian gravity be generalised to include not only bodies with mass but energy also?Thank you.Can my thread be moved to classical physics?
  6. Adams2020

    I The center of mass & relativistic collisions

    In special relativity (especially relativistic collisions), is the center of mass frame as useful as Newtonian mechanics?
  7. K

    I Tau mass -- How was it measured for the first time?

    Hello! How was the tau massed measured for the first time? I read that tau was discovered by ##e^+e^-## collisions and they looked for an excess of of end products containing an electron, a muon and some missing energy (coming from the decay the 2 resulting tau's). But the missing energy would...
  8. Andrei0408

    Centre of mass of two boaters in a small rowboat

    If I calculate the cm pos vector using the two boys' masses, I get 2m, which is the distance between them, but I don't know how to find the boat's displacement when they switch places. How do I represent the fact that they switch places? In what form?
  9. M

    A Claimed derivation of Weinberg angle, Higgs/W mass ratio

    https://arxiv.org/abs/2010.15621 Superselection of the weak hypercharge and the algebra of the Standard Model Ivan Todorov [Submitted on 29 Oct 2020] I haven't had time to study this paper yet. But a few curiosities: It talks about Clifford algebras. But in fact it builds on work due to...
  10. S

    B What can be interpreted if mass of product < mass of reactant?

    Can I just interpret that some of energy of P + Q (maybe KE) is converted into mass of X + Y? Another question: is it possible that mass of products = mass of reactants? Thanks
  11. Z

    Are Olympic weightlifting records based on mass or weight?

    Since we have a .3% change in weight (force) for weights that are lifted from locations on earth, are their rules that focus on mass or weight with olympic weightlifting? In other words, if i wanted to break the world squat record, wouldn't i go to the equator to try and break it, giving that...
  12. K

    I Geodesics using 2 Variables: Time & Radius from Mass

    *Moving this thread from 'General Math Forum' to 'General Relativity Forum' in order to generate more discussion.* Any object will move through spacetime along its geodesic. Since mass bends spacetime, an object initially at rest near the mass will move towards the mass along a geodesic. It...
  13. MJNZ1

    What is the correct formula I should use? (measuring g using a swinging mass)

    Hi, This is my first post, I hope I have done it right. The top mass is represented as m and the weight hanger M.The image below is my attempt with the first formula 2. I have done it in grams because when I did it in kg's it was not anywhere near 9.81ms^-2...I know it is wrong :) g exp. =...
  14. Hamiltonian

    Doubt related to the velocity of the center of mass

    In question 1. since there is no external force on the system of particles(and since it was initially at rest) shouldn't the ##V_{cm}## be zero? But the correct answer applies the above stated formula for ##V_{cm}## and gets ##V_{cm} = v/2## and in question 2 again as there is no external force...
  15. M

    B Mass of Hanging Rope: Calculate Easily

    Hi, I have a question about a hanging rope - how do you find it's mass? I've been searching a long time, stumbled across some advanced calculus involving catenary functions and equations, but couldn't quite figure it out.
  16. S

    Determining net force and acceleration

    Hi All, Please see attached photo of the question. It is asking for net force and acceleration. Taking the forces acting upwards and downwards on the parachutist as vectors: for A the net force would be 800-300=500; B would be 0 and C; would that be 800-1500=-700? And if so would that imply...
  17. Adams2020

    Mass difference due to electrical potential energy

    I do not really know the relationship between potential energy and mass difference. Isn't the difference in mass of protons and neutrons due to their quarks? (the neutron is made of two down quarks and an up quark and the proton of two up quarks and a down quark.) Please help.
  18. Hamiltonian

    Gram atomic mass -- what exactly is it?

    It is stated that the gram atomic mass of an element is its atomic mass represented in grams. The gram atomic mass of sodium is said to be 23g (isn't this number way to big to represent the mass of an atom?!) but if its the mass of one mole of sodium it makes sense(but won't that be molar mass)...
  19. M

    Mass moment of inertia of a composite shape

    My thought process was to get the mass moment of inertia of the rectangle and then subtract the mass moment of inertia of the quartercircle from it. The MMoI of the rectangle is: (1/3)(0.005*7850*.6*.3)(.3^2)= 0.212 meters The MMoI of the quartercircle is: (1/4)(0.005*7850*¼π 0.3^2)(.3^2) + ? My...
  20. S

    Acceleration of a spring - mass system

    m1 = top left m2 = bottom left m3 = top right m4 = bottom right My questions: 1. Will all the object (m1, m2, m3,and m4) have same acceleration? 2. Should I assume initial extension of both spring is the same? (only based on the picture) 3. Will the extension of the spring change after the...
  21. htam9876

    I The Energy - Momentum Equation vs the Energy - Mass Equation

    First, introduce the energy – momentum equation E² = p²c² + (m0c²)². Next, just think it in natural way. If the energy – momentum equation reflects the stationary situation, then, momentum p naturally equals to zero. Then, we got E² = 0 + (m0c²)², namely: E = m0c². It can be denoted exactly...
  22. A

    I Question Regarding Determining the Mass of Venus

    Venus is in the news! I looked up this well-regarded paper by A. S. Konopliv, W. B. Banerdt, and W. L. Sjogren Venus Gravity: 180th Degree and Order Model They list values for GM (see attached picture), such as GM 324858.63 ± 0.01 so in principle calculating M should be trivial. The problem...
  23. jim mcnamara

    Carnian Pluvial Episode newly identified mass extinction event

    https://phys.org/news/2020-09-discovery-mass-extinction.html This article discusses a newly identified extinction event that occurred in middle Triassic. Mammals appeared at the end of the event, dinosaurs which were rare, became the dominant animal group. The cause was massive eruptions in...
  24. P

    Finding the reqiured fuel mass for a nuclear reaction

    Hi I need to find the amount of fuel needed for a nuclear reaction to produce 800MW daily . The reaction is n + 𝟗𝟒𝑷𝒖 𝟐𝟑𝟗 → 𝟓𝟐𝑻𝒆 𝟏𝟑𝟒 + 𝟒𝟐𝑴𝒐 𝟏𝟎𝟑 + 𝟑 𝒏 Can you please give me a hint on how to do this? Thank you very much for your help
  25. M

    I Majorana Mass Plot: Normal & Inverted Hierarchy

    Hello! In the attached plot, we have the Majorana mass as a function of the lightest neutrino for the normal (m1<m2<m3) and inverted (m3<m1<m2) hierarchy. Plugging in the values from the PMNS matrix in the formula for Majorana mass, I get something of the form: ##m_{\beta\beta} =...
  26. Hamiltonian

    Finding the center of mass of a solid hemisphere

    for this derivation, I decided to think of the solid hemisphere to be made up of smaller hemispherical shells each of mass ##dm## at their respective center of mass at a distance r/2 from the center of the base of the solid hemisphere. also, I have taken the center of the base of the solid...
  27. PainterGuy

    Electromagnetic mass of an electron

    Hi, I was reading the following Wikipedia article and couldn't make sense of few points. I'd appreciate it if you could help me with it. Source: https://en.wikipedia.org/wiki/Electromagnetic_mass#Rest_mass_and_energy Question 1: What is this "electrostatic energy ##E_{em}##"? Is it some kind...
  28. K

    B Earth Center of Mass: GR & Inertial Object Acceleration

    Super-basic question that I'm embarrassed to ask. It's just what the summary says: Taking Earth's center of mass as our reference frame, how does GR account for an inertial object near the surface approaching with an acceleration of G? I assume (perhaps incorrectly) that this is an inertial...
  29. Frouel

    How can I solve this physics problem step by step?

    I attended to many attemps and I not able to find out no dependencies in this layout. Does someone can show me how to solve this problem step by step? What we must take into considarion in solving such tasks?. How to start?. I got stuck. This task is from Polish Physics Olympics.
  30. Like Tony Stark

    Write the equations of a mass and spring in different accelerated systems

    Hi I know that the equation of a simple harmonic oscillator is ##\ddot x + \omega^2 x=0##. The thing is that I don't know how to get to that equation in the situations given. In the first situation, I know that ##x) k(x-x_0)=m(\ddot x -x \dot \theta ^2)## ##y) N=m(2 \dot x \dot \theta)## So...
  31. PainterGuy

    Why wasn't fluorine used as a standard for atomic mass?

    Hi, I found the two sections in red a little confusing. I'd appreciate it if you could help me with it. Source: https://en.wikipedia.org/wiki/Atomic_mass#History The existence of isotopes was first suggested around 1913[reference]. The first periodic table by Mendeleev in 1869 used...
  32. sbrothy

    Apropos Raspberry PI DIY Mass Spec using Raman Scattering

    https://hackaday.io/project/1279-ramanpi-raman-spectrometer It's a pretty nifty gadget this Raspberry thingy. A computer the size of a pack of cigs. :) And a mass spectrometer... I'm not sure what such a device costs but I'm sure it pretty frigging expensive!
  33. Leo Liu

    Discontinuity of velocity in a problem on mass flow and momentum

    In this question, the particles are constantly transmitting their momentum to the rocket. The force required to keep the rocket stable can be express as ##\vec F=(\vec v-\vec u)\dot m##. However, when I tried to solve this question using the Newton's 2nd law, I found that the infinitesimal...
  34. LCSphysicist

    Hanging Spring with non-negligible mass is subjected to a driving force

    First i will use a equation resulted in considering a spring as a continuum limit of massive mass: ω = √(KL/ρ)*kn ρ is the linear density ρ ω = √(KL/ρ)*kn X = A*cos(kn*x)*cos(ω*t) ξ = A (first consequence) X = ξ*cos(kn*x)*cos(ω*t) ∂y/∂x need to be zero in x=L (for strain be zero) kn*L =...
  35. Hamiltonian

    Two pulleys lifting a mass in parallel

    if the ends P and Q are being pulled down with a uniform speed its acceleration is zero and hence the Tension in the string will also be zero and if this is the case which force will make the block of mass M rise? is this a fatal flaw in the question?
  36. madafo3435

    Angular momentum: Grooved cone with a mass sliding down the groove

    .
  37. burian

    Trajectory of a mass element in a string overhanging a pulley

    Hello everyone, this is a thought experiment I made, it involves two ropes being pulled of a pulley similar to an atwood machine, and a block attached to the two pulleys at the other end. The ropes are being pulled at a constant velocity $ U$ from the end away from the block and the block rises...
  38. J

    I Changing the effective mass of an electron using electric potentials?

    The Dirac equation for an electron in the presence of an electromagnetic 4-potential ##A_\mu##, where ##\hbar=c=1##, is given by $$\gamma^\mu\big(i\partial_\mu-eA_\mu\big)\psi-m_e\psi=0.\tag{1}$$ I assume the Weyl basis so that $$\psi=\begin{pmatrix}\psi_L\\\psi_R\end{pmatrix}\hbox{ and...
  39. Helena Wells

    I Mass of the Moon and Gravitational Lensing

    During an eclipse the Moon covers the Sun.However this shouldn't be happening due to gravitational lensing we should be able to see some light? Is the mass of the Moon not big enough or photons do reach us but they are so little our eyes can't detect them?
  40. M

    Calculating Final Positions & Velocities for M1, M2 & Spring After DeltaT

    Let's say you have two masses on either side of a spring. Mass 1 is connected to the end of a spring. The spring itself has no mass. Mass 2 is free in space. So you have: [M1]-[spring] [M2]So it's more descriptive, I'll name the variables like you might in programming. Let's define...
  41. Nexus99

    Moment of inertia, center of mass and vincular reaction of a rod

    I'm struggling doing point 5, i have no idea how to solve that question. In point 1 i obtained the following result: ## I=\frac{ML^2}{2}## calculating the integral of dI, the infinitesimal moment of inertia of a small section of the rod of length dr. 2) Through the conservation of angular...
  42. Kiah Palmer

    Chemistry Mass of an element required for a chemical reaction equation

    Conversion: 9.65 kg = 9650 g Mass Al = 26.98 g/mol Molar Mass Al2O3 = (2 x 26.98) + ( 3 x 16.00) = 101.96 g/mol Mol Al2O3 = 9650 g / 101.96 g/mol = 94.65 mol Mol Al Required = 94.65 mol x 2 = 189.3 mol Mass 100% Al required = 189.3 mol x 26.98 g/mol = 5.107x103 g Mass 80% Al required =...
  43. Hamza M khan

    The center of mass of a semicircular arc of non-negligible width

    My attempt: 1) I am going to start this with a goal of setting up a reimann sum. First I divide the "arc"(?) of angle pi into n sub-arcs of equal angle Δθ 2) The total center of mass can be found if centers of mass of parts of the system are known. In each circular arc interval, I choose a...
  44. Kiah Palmer

    Chemistry Homework Help: Calculating Mass from Chemical Reaction Equations

    1a) Step 1: Balance the equation - S8 + O2 -> SO2 = S8 + 8O2 -> 8SO2 Conversion (t to g) 6.00 t = 6x10^6 g Molar mass SO2 = 23 + (2 x 16) = 64 g/mol 6x10^6 g / 64 g/mol = 9.375x10^4 mol SO2 reqired amount Sulphur = 9.375x10^4 mol / 8 mol = 1.172x10^4 mol S8 Molar mass S8 = (8 x 32)...
  45. Justinboln

    Calculate the New Velocity and the Velocity of a Pendulum Mass

    Question 1: A pendulum 2.2m long has a mass of 8.5kg suspended from it. The pendulum is initially in a vertical position and is moved to new position 35 degrees from the vertical. (a) How much work is required to move the pendulum to its new position? (b) If the pendulum swings from this...
  46. LCSphysicist

    Analyzing Net Forces and Equations in a Driven Mass on a Circular Path System

    What you think about this system:? F*cosw - k(x1+x2) - k(x1-x2) = mx1'' -k(x1+x2) - k(x1-x2) = mx2''
  47. udtsith12

    Mass loss in Bernoulli's Principle?

    Hi, I could really use help. I am trying to understand what would happen to the velocity of a freestream air if it loses mass while traveling down a tube. For example, suppose that you have 1 cubic meter of air traveling at 10 m/s down a duct with a 1m^2 cross section. And then suppose that you...
  48. LCSphysicist

    How to calc the period of this mass spring system?

    This is a problem very easy to deal with if we consider the effective spring constant, however, i want to avoid this solution, and see how to justify the period of this motion just by analyse the forces or the energy, what seems a little hard to me. First of all we would need to find the force...
  49. H

    I Mass Unit in General Relativity

    James Clerk Maxwell deduced that the unit of mass has the dimensions of (L^3)(T^-2). But he assumed Newton's Law. What would it be under general relativity?
  50. Nexus99

    A falling rotating rod strikes a ball of mass M....

    A homogeneous rod of length l and mass m is free to rotate in a vertical plane around a point A, the constraint is without friction. Initially the rod is stopped in the position of unstable equilibrium, therefore it begins to fall rotating around A and hits, after a rotation of ## \pi ## , a...
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