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. A

    B Mass transfer between neutron stars in a binary pair

    When we read about the mass transfer between neutron star pairs in a binary system, how is it that the one receiving the matter can increase its spin rate. Adding mass to a spinning object ought to slow due to conservation of momentum. Where does the energy come from?
  2. P

    How does a mass moving up a ramp change its velocity?

    A point mass is moving at speed v, on a horizontal plane, until it reaches an incline. Immediately after just climbing up the incline, its speed remains at v, but its direction changes. How does this happen? Q2: Now, I drop a point mass such that it falls vertically downward onto a fixed ramp...
  3. Y

    Mass slipping on a moving inclined plane

    Body A rests on a inclined plane of body B . the angle of slope is α , the coefficient of friction between the two bodies is μ . Body A does not slip on body B because we accelerate body B with a. What is the minimum and maximum acceleration required for body A not to slip? What will be the...
  4. jim mcnamara

    Ordovician mass extinction second wave - deep sea anoxia

    https://www.nature.com/articles/s41561-021-00843-9 Popular science version: https://scitechdaily.com/uncovering-the-surprising-secrets-behind-Earth's-first-major-mass-extinction/ Nature paper discusses causes of the second "wave" of mass extinction at the end of the Ordovician (~445mya) Really...
  5. J O Linton

    B Spatial curvature around a spherically symmetric mass

    Suppose I measure the circumference of a circular orbit round a massive object and find it to be c. Suppose I then move to a slightly higher orbit an extra radial distance δr as measured locally. If space was flat I would expect the new circumference to be c + 2πδr. Will the actual measurement...
  6. Z

    Mass matters for standing waves on a string?

    The question is to explain the equation of motion of the red ball. The string is massless and a small ball of mass m is attached to the string halfway. I just assumed the mass of the string is the same as the mass of the ball and explained the equation A cos(Wt) by defining the terms. I'm not...
  7. V

    Hinged rod rotating, falling and hitting a mass

    Assuming no friction anywhere, no drag and perfect inelastic collision Using conservation of mechanical energy i can determine the rotational speed of the rod right before collision occurs. mgh=1/2*i*w^2 center of mass falls 1/2*L so we have: M*g*1/2*L = 1/2*(1/3*M*L^2)*w^2 Solving for w...
  8. D

    Reverse Mass Drivers: Catching Surfaces Grazing Orbiting Spacecraft

    If a mass driver could theoretically launch a vehicle then surely it could catch one too. Anyone know about articles related to mass drivers that refer to catching surfaces grazing orbiting spacecraft ?
  9. vipers120

    I Modeling a (rotating) mass impact on a preloaded (rotational) spring

    I am trying to model numerically the following system: A rigid body mass is rotating freely around an axis (no rotational stiffness/damping) within a range, let's assume plus-minus 3 degrees for now. Case A. The external forces on the mass are low and keep changing which results in the situation...
  10. J

    A Charge conjugation in quantum gravity

    The charge associated with gravitational interactions is the mass. In the Standard Model, charge conjugation is the "flippin" of all kinds of charges (electric, color, etc). So, if we were to, say, incorporate quantum gravity in a beyond the Standard Model theory, what would the full charge...
  11. L

    Velocity of a mass m that moves along the x-axis

    dv/dt(mv^2-mv0^2) = dv/dt(kx0^2-kx^2)
  12. applesoranges

    Mass swinging in a horizontal circle on 2 strings

    I have already solved this problem, just would like to double check something with you conceptually. I've got a negative result for the tension in the lower cord. Intuitively I think it is right, because the lower cord does not support the ball in its opposing the force of gravity. It actually...
  13. Leo Liu

    How to define the mass ratio of a multi-stage rocket?

    Sutton writes that the mass ratio of a multistage rocket is the product of the individual vehicle stage mass ratios, does it mean the expression below? $$MR=\prod_{i} \frac{m_{f,i}}{m_{0,i}}$$
  14. CynicusRex

    Chemistry Calculating the mass percent from a given volume % and density

    [I've solved b, but can't figure out a for the life of me. I have a couple of attempts, but it's just nonsense, it's like I've short circuited.]
  15. strangerep

    A Proof that neutrino flavor oscillation implies nonzero neutrino mass?

    [This is a reference request.] I'm dissatisfied with the "proofs" I've found so far. E.g., in Kayser's review from 2008, in the paragraph following his eq(1.4), he assumes a propagation amplitude Prop##(\nu_i)## of ##\exp(-im_i \tau_i)##, where "##m_i## is the mass of the ##\nu_i## and...
  16. L

    Gravitational force - I translating the wording into the formula

    i spoke to my proffesor about it but all he said was to put 1 in m1 and m2... for r^2 since it says to quadruple to just put 4^2 I asked about the G in the equation but he said not to worry about iit and pretend its not there...
  17. S

    Force exerted by rod on a mass moving in vertical circle

    (A) and (B) are obviously wrong but I think both (C) and (D) are correct. At the top, the forces acting on the mass are tension and weight, both directed downwards so the equation of motion will be: $$\text{Tension}+\text{Weight}=m.a$$ $$\text{Tension}=m.a-\text{Weight}$$ Based on that...
  18. brotherbobby

    Does Dropping the Anchor Affect the Barge's Water Displacement?

    (I must confess before I can begin that I found this problem difficult to understand, for reasons I will make clear below. I know it appears simple.) Attempt : Let me begin by drawing the problem situation alongside, to the best I understand. We can see that the in both cases (i) or (ii), the...
  19. haruspex

    Insights Corrections to MIT Open Courseware: Systems of Varying Mass

    Continue reading...
  20. jaumzaum

    A Motion of a spring that has mass

    Hello! I was trying to find the equations of motion for a spring with uniform distribution of mass (uniform just in t=0, because after a while the distribution will be non-uniform). I tried to attack this problem first in the discrete (non-continuous) way: "Consider N springs with elastic...
  21. T

    Circular motion of a mass on a string on an inclined plane

    (I drew motion in the opposite direction so the object would rotate trigonometrically but it should be the same thing) I have just finished the Kinetic Energy and Work chapter in my course and this is the last problem from the problem set. I have not worked many problems with the Work-Kinetic...
  22. L

    Amplitude of oscillation of a mass which is the pivot of a pendulum

    1) By conservation of mechanical energy we have ##m_2gl(1-\cos(\alpha))+m_1gl=\frac{1}{2}m_1v_1^2+\frac{1}{2}m_2v_2^2+m_1gl## and by conservation of linear momentum along the x-axis we have ##m_1v_1+m_2v_2=0## which gives us ##v_2=\sqrt{\frac{2m_1gl(1-\cos(\theta))}{m_1+m_2}}## and...
  23. S

    I Reduced mass to bind hyper- and mesonuclei

    A deuteron is a bound hexaquark. Since both triquarks have severally masses of about 940 MeV, the reduced mass of a deuteron is under 470 MeV. Deuteron is bound... but only feebly. It has only one bound state: ground state orthodeuteron. All excited states of orthodeuteron are unbound...
  24. Ranku

    I Is Dark Matter Composed of Low-Mass Particles?

    Does the diffused distribution of dark matter as halos over galaxies imply dark matter is made up of low-mass particles?
  25. A

    Semi empirical mass formula derivation help

    Can somebody please derive for me an example of the Binding energy from the Semi Empirical mass formula? I am trying myself but always there is a difference between the database binding energy and my own result. I am calculating the BE of Niobium 93. For the mass formula I used the coefficients...
  26. Istiak

    Why position times mass is equal to 0 here (vanishes)?

    $$\sum_i m_ir_i$$ Why the term always vanishes? There's some more equations where the mr was vanished. But, they didn't explain why it vanish. Why the term vanish? I think that's for position 0,isn't it?
  27. L

    Mass m sliding without friction inside a rotating tube

    1) To be in equilibrium, it must be $$\begin{cases}F_{centr}-T=0\\ T-mg=0\end{cases}\Rightarrow F_{centr}=T=mg\Rightarrow m\omega^2 R_0=mg\Rightarrow R_0=\frac{g}{\omega^2}$$ 2) It is intuitive that this equilibrium is unstable but I don't know how to formally prove this. 3) In ##R_0## the...
  28. W

    I Does a Magnet Curve Spacetime More Than a Non-Magnetic Mass?

    Hi. My question is described in the summary. I'm seeking some advice. The Reissner-Nordstrom solution for charged spherical bodies seems to indicate that electrostatic fields will be a source of gravitation. I've not seen anything similar for magnetic fields but I can't imagine how it could be...
  29. C

    Maximum safe mass of an asteroid in geostationary orbit

    Summary:: What is the maximum safe mass of an asteroid in geostationary orbit before it causes problems? Hello everyone, If there was an asteroid in geostationary orbit around the Earth, over the Pacific Ocean, what would be the highest mass it could have before it would start having...
  30. A

    I Forward momentum of mass due to inertia

    Help me understand a concept I came across by accident. So there is an axis (red) that is rotating with two rods attached to it (45 degrees from axis and 90 degrees with respect to one another) now if the balls at first are located closest to the red axis , as the axis begins to rotate the balls...
  31. Ebi Rogha

    I Mass of Water Increasing with Heating

    Suppose we heat up a sealed container of water (no vapour escape), will it mass increase according to E=m.c^2 ?
  32. ergospherical

    A Rate of Change of Bondi-Sachs Mass: Derivation Reference

    If ##(u,v)## are null coordinates and ##S(u,v)## a two-surface of constant ##u## and ##v## then the Bondi-Sachs mass ##M_{\mathrm{BS}}(u) = -\dfrac{1}{8\pi} \displaystyle{\lim_{v \rightarrow \infty}} \oint_{S(u,v)}(k-k_0) \sqrt{\sigma} d^2 \theta## satisfies (Poisson, 2007)\begin{align*}...
  33. T

    I Does Special Relativity Affect Mass?

    Is mass relative? does the faster you go change your mass? Because according to the Energy calculations E = ymc^2 at speed and mc^2 and since the speed of light is constant, does that mean that mass changes? [Thread edited by a Mentor to remove personal speculation]
  34. Safinaz

    Understanding the Mass-Length Relation: Solving for V in Simple Equation

    Hello, If i have this relation: ## M_p^2 = M^3_s V ## where ##M_p ## and ##M_s ## are masses in GeV and V is a length. Let ## M_p = 10^{18} ~ ## GeV and ##M_s = 10^3 ## GeV , what is V in meters ? My solution : The equation becomes ## V = 10^{30}## GeV , but ## 1 m \sim 10^{15} ~...
  35. dabbih123

    Find the unknown mass on a inclined rope pulley system.

    First I calculated the forces that were working against mass B. m(A)g sin 30 + μm(A)g cos 30 = 12.86 N The force working with mass B is m(B)g = 9.8m(B) I thought I could solve for B using F=ma where 12.86 N = (2kg+m(B))*(0.58), but of course, 12.86 N is just the force required to make the...
  36. crudux_cruo

    B Torque applied by a continuous mass instead of point particle

    I came across this 'problem' when I was trying to think about how a torsion spring would apply torque in something like a miniature catapult. I understand that in the context of something like turning a wrench, we can find the net torque on the wrench by treating the hand applying the force as...
  37. S

    I Counter-rotating mass to counteract inertial spin

    How do I determine the required combination of spin rate and disc mass to counteract the inertia of a second spinning disc? I have complete knowledge of and control over both disc masses and spin rate and geometry. Let's say Disc A geometry, mass and spin rate are fixed and constant, so I can...
  38. R

    Force Diagrams for a Combined Mass

    I know that the ##F_{AonB} = -F_{BonA}##, but I just wanted to check something. If object A is the truck, then the x-direction should have a vector coming from the force of the engine driving the truck forward, a vector pointing in the negative direction for friction, and a vector in the...
  39. ayans2495

    Hiking the Appalachian Trail: A Beginner's Guide

  40. nazmulhasanshipon

    Finding out the rotational speed of a mass

    **My Attempt:** Here, I considered for 2 kg mass the resultant motion is zero, which means it's acceleration (a) would be zero. So, if we consider the Tension force from the 1.5 kg mass to keep 2 kg mass from falling is L, then 2×9.8-L=ma=2× 0 ⇒ L=19.6 N. But where does the tension force from...
  41. nuckshuck11

    B Lifting an object with a mass difference of just 1kg

    Hello, can anyone help me out with this? If i want to lift an object that weights 100kg and I am going to do it with a 101kg of force (990,81 N ). Then my acceleration would be; a = F/m a= 990,81N / 101kg = 9,9081 m/s2 but gravity is pulling it down so then I am acually accelerating it with...
  42. chwala

    Solving this rate of decay problem -- Mass loss calculation

    My interest is on question ##11.ii## only. I think there is a mistake on the markscheme...i just need a second opinion on this...find attached the question and markscheme... markscheme here: it ought to be, ##e^{0.0277t}=1.6797##
  43. Paige_Turner

    B Why Does Mass Pull on Other Stuff?

    Why doesn't it repel things... or just pass through and leave distance unchanged?
  44. mfb

    I New cosmological neutrino mass constraint: sum<0.09 eV at 95% CL

    arXiv: On the most constraining cosmological neutrino mass bounds From neutrino mixing we know that an inverted order (two "heavy" neutrinos, one light neutrino) needs a sum of masses of at least ~0.09 eV, while the normal order (two light, one "heavy") can have a sum as low as ~0.05 eV. The...
  45. ZurraMath

    Please check my solutions -- Mass being pulled with an angled rope

    A block of mass M = 4 kg is pulled by a force F = 100 N forming an angle of 60 degrees with themhorizontal plane with friction coefficient 0.3. Determine the work of force F, friction force and normal force.
  46. nonamebrand

    B Can particles interact without a mass?

    I recall reading someone questioning if it were possible for the higgs boson to be the primordial atom which led to the start of the universe. I was just wondering if that could even be possible, since the higgs field was zero and couldn't have given these particles any mass. (please be kind...
  47. Istiak

    Find the center of mass of an arc

    In my mind, I had cut half of B and, thought it's semi-circle. Then, I was trying to find Center of Mass by taking it as semi-circle. But, I get an answer which is approximately, close to main answer. Someone else had solved it another way This way I can get the accurate answer. But, the...
  48. K

    I How does inertia, a property of mass, arise?

    Do todays physicists have a deeper understanding on mass and inertia on how inertia arises?
  49. wrobel

    A The equations of variable mass systems

    The equations of variable mass systems are usually deduced from some very informal argument. It is so at least for the books I know. So I tried to construct a formal proof based on the continuous media equations. Criticism, remarks etc are welcomed. Let ##D\subset \mathbb{R}^q## be an open...
  50. I

    ODE solver for second Order ODE with Stiffness and Mass Matrices

    i am new to MATLAB and and as shown below I have a second order differential equation M*u''+K*u=F(t) where M is the mass matrix and K is the stifness matrix and u is the displacement. and i have to write a code for MATLAB using ODE45 to get a solution for u. there was not so much information on...
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