What is Mass: Definition and 1000 Discussions

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. SamRoss

    I Still have questions about photon mass

    Just read the FAQ post "Do photons have mass?" and I'm still confused. The post says that all of the photon's energy is in the pc term of the energy-momentum equation. (1) But isn't p equal to mv, implying there is mass? (2) The post also says there is no inconsistency with E=mc^2 but doesn't...
  2. I

    I Invariant mass plots for resonance 'particles'

    The interaction p + π- → n + π- + π + may proceed by the creation of an intermediate 'particle' or resonance called a rho. This can be detected as a peak in the plot of invariant rest mass energy of the emergent pions versus frequency of pions observed. My question is quite simply, invariant...
  3. J

    I Which object will hit the surface of a planet first?

    If we have two objects A and B appear on the opposite sides of the equator of a planet like Earth with the same mass as Earth. Object A is a neutron star with the mass of the sun and object B is a iron cube with the mass of one gram. Will A or B hit the Earth at the same time or will one hit...
  4. Islam Hassan

    I Mass Equivalence of Photon Content Inside the Sun?

    If it takes anywhere between 5,000 to a couple of hundred thousand years (various internet sources have various values) for photons generated in the sun’s core to reach its surface and radiate out, what is the estimated mass equivalence of all these photons making their way out from the core to...
  5. dRic2

    Mass and energy balance equations for a tank filled with H20

    Hi, this problem should be very simple: I have a tank containing water. (going in and out). I want to write the differential equations to see what happen to the temperature and the level of the vessel if the flow of water is not constant. the system should be: $$A \frac {dl} {dt} = F_{in} -...
  6. A

    Thermodynamics problem -- Find the mass of water that vaporizes

    Homework Statement Find the mass of water that vaporizes when 3.02 kg of mercury at 223 °C is added to 0.347 kg of water at 83.4 °C. Homework Equations Mercury Q = Water Q + Water mL mc∆t= mc∆t + mL The Attempt at a Solution mass of vapor = ((3.02)(140)(223-tfinal) - (4186)(.347)(change in...
  7. S

    I Turning mass Energy calculation

    Hello, can someone tell me how, or provide me a formula, to calculate the power of the turning shaft? in Nm or Watts, I don't mind. The mass (23Kgr) is turning at stable speed of 100 rpm by external independent force. The shaft is supposed to be on bearings both sides.. I made a picture to save...
  8. C

    I Distance between two nucleons

    The potential energy associated to the interaction between nucleons has its minimum (point of equilibrium) at ##r\sim 0.7 fm##, as showed in the following graph: Nevertheless, there are two facts that are, apparently, in contrast with this: - The average distance between nucleons is...
  9. Islam Hassan

    I If the Universe’s Mass was 100 At the Moment of the Big Bang....

    Supposing that the total mass + energy content of the Big Bang was 100 in energy-equivalent terms. What would we consider its energy-equivalent mass to be today? If the universe is today accelerating and that acceleration is not abating, then (naïvely perhaps...) its (dark-energy) potential...
  10. C

    I Pauli principle and coupling term in Weizsäcker formula

    Consider the pairing term in Weizsäcker formula. Here https://en.wikipedia.org/wiki/Semi-empirical_mass_formula#Pairing_term it is claimed that: I don't understand how Pauli exclusion principle should be the cause of this. This term comes from spin-spin interaction (or "coupling"), but I do not...
  11. R

    B 2 large objects of equal mass, Will they move each other?

    Suppose there are 2 planets the size (diameter) of Jupiter. Both have the exact same mass. They are separated by a distance of about 10 times the diameter of the planet. They are both at rest. Now, will they start moving towards each other or stay in the same place? This is a sort of thought...
  12. barryj

    Finding the Velocity of a Mass in Circular Motion

    Homework Statement See attached diagram and statement of problem Homework Equations Conservation of momentum ... mv = MV + mv/2 mv/2 = MV V = mv/(2M) centripetal force...centripetal force equals weight at top of circle. MV^2/L = Mg V^2 = Lg V = (Lg)^.5 The Attempt at a Solution Set V = V...
  13. prakhargupta3301

    Exploring the Relationship Between Velocity and Displacement in Pulley Systems

    Homework Statement Homework Equations xcxcxcxcxcxcxcxcxcxcxc[/B]The Attempt at a Solution My attempt: Let displacement of A be x m, Let displacement of B be y m, and Let displacement of C be z m. Step2: [/B]a+b+c+d=(a+x-y)+(b+x)+c+(d+z) 2x-y=-z Differentiating LHS and RHS components...
  14. A

    Gravity of the Earth if its mass were doubled

    What would be the value of gravity on the surface of the Earth if its mass was twice as large and its radius half of what it is now?
  15. L

    Center of Mass Balancing Question

    The question is: The orange and blue cat are currently balanced on the see saw. The orange cat then eats a bird, which of the following could make the see saw balanced again? - I attached the picture that the question is referencing. And the possible answers are: A. Orange cat stays at same...
  16. B

    Use triple integral to find center of mass

    Homework Statement Find the centre of mass of a uniform hemispherical shell of inner radius a and outer radius b. Homework Equations ##r_{CoM} = \sum \frac{m\vec{r}}{m}## The Attempt at a Solution Using ##x(r,\theta,\phi)## for coordinates...
  17. P

    Energy problem with 2 objects (a mass flying vertically off of a ramp)

    Homework Statement Consider a platform (mass: M) which horizontal surface AB s smoothly joined to vertical surface CD as shown in the figure below. Initially, the platform is fixed in place on a horizontal floor. A small object (mass: m) is placed on AB and given an initial speed of v in the...
  18. H

    Melting time vs Temperature and Mass

    I recently saw the movie “Man of Steel”. In Superman’s fight with Zod, Superman cuts (by melting) a steel I-beam, that Zod is about to hit him with, with a swipe of his heat vision. To melt steel that fast (under 3 seconds) requires a large temperature. My question is how can we calculate the...
  19. W

    2 weights on strings, 1 attached to pulley, the other end anchored

    Homework Statement https://imgur.com/jE8SMDR That's a drawing of the problem. I need to solve for the ? weight. Homework Equations not sure The Attempt at a Solution none, I don't want the answer, I just want the relevant equations. I haven't taken physics in a few years though (I'm out of...
  20. V

    An object of some mass, m, is accelerated upwards....

    Homework Statement an object of some mass, m, is accelerated upwards (from rest) off the surface off the Earth for some unknown time, t. At the end of this time, the object is traveling at some new speed, x. Derive the following formula. That is, show that no matter how much time the rocket...
  21. R

    Calculating the mass of an object

    Homework Statement A dog runs 480m in 28 seconds , we’ve to work out the mass of the dog Homework Equations F=ma [/B] M=f/a The Attempt at a Solution Really at a cross roads as every angle I work at this I need the mass of the dog to calculate the other components , a simple yes or no...
  22. C

    Length Contraction/Relativistic mass question

    Homework Statement The proper length of spaceship A is 60.0m and the proper length of spaceship B is 120.0m. The proper mass of spaceship A is 15000 kg. An observer on Earth watches the two spaceships fly past at a constant speed and determines that they have the same length. If the speed of...
  23. S

    Two elastic ropes, Acceleration and Height Problem

    Homework Statement As on the paper below: Homework Equations Suvat? The Attempt at a Solution As on my paper a) I think I got the acceleration correct by measuring the angle, halving the angle to get the force upwards by each rope. Or is that the wrong answer? b) Should be half as it’s...
  24. J

    Find mass of a rope pulled by a force

    Homework Statement Homework EquationsThe Attempt at a Solution The force F exerted by the wall on the left end of the rope will make an angle 30° with the vertical . If we do the force balance , F sin30° = 20 Fcos30° = Mg This gives M = 2√3 Kg . This gives 3.5 Kg . But answer given is...
  25. S

    Finding the change in mass of a charged body if it loses 1 C

    Homework Statement The mass of an electron is 9*10^-31kg. Find the charge in mass of a charged body if it loses 1 Coulomb of negative charge. Use your answer to explain why electricity was originally thought to be weight less. 1 coulomb = 6.642*10^18 elementary charges. Homework Equations...
  26. Andres Padilla

    Find the mass M so that the net torque is zero

    Homework Statement Hello, I have a problem I don't want how to approach, it is a little weird. It is a problem of equilibrium (torque) The situation and my approach is in the picture I uploaded. A beam is supported by the blue structure. On the beam it is a person(100N) at a distance of 3m in...
  27. B

    How does the incline of the rod depend on mass and force F?

    Homework Statement We have a rod with length L and with the left end the rod is fixed to the ceiling in such a way it can swivel. As we can see from the picture (attached file) on right end two forces are acting on the rod: F and mg. The question is: How does the incline of the rod depend on...
  28. Nojins

    Determining the angle for a mass to overcome friction

    Homework Statement A crane is moving two equally spaced masses to the roof. One box is 10kg and the other box is 20kg. As the plank tilts towards the 20kg box, at what angle will each box begin to slide? The coefficient of static friction is 0.4 Homework Equations Newton's second law, Fnet=ma...
  29. JorgeM

    I Is this expression for Mass Flowing Out of a Bottle correct?

    Hello there, I am going to implement a numerical method to solve how much Mass of a fluid has gone out of an opened bottle. I am going to get h(t) with some sensors but I am not sure if this expression for Mass gone out "M" is correct. The area of the bottle at the up part. A1 The density of the...
  30. LesterTU

    How to evaluate the effective mass tensor (band structure)

    Homework Statement The energy-band dispersion for a 3D crystal is given by $$E(\mathbf k) = E_0 - Acos(k_xa) - Bcos(k_yb) - Ccos(k_zc)$$ What is the value of the effective mass tensor at ## \mathbf k = 0 ##? Homework Equations The effective mass tensor is given by $$ \left( \frac{1}{m^*}...
  31. C

    How Much Mass Converts to Energy in a Nuclear Plant Over a Month?

    Homework Statement A nuclear power generating station generates 3.0 x109 W of power. How much mass does the plant convert into energy each month (30 days)? Assume that the process is 100% efficient[/B] Homework Equations E = mc2 EJ = (Pw)( ts) The Attempt at a Solution First determine the...
  32. bbbl67

    I Relationship between stellar mass and core mass?

    Is there an astrophysical relationship between the how large a star's core gets and how large the star itself gets? Is it a simple linear percentage, or something more complex? For example, red dwarfs can fuse their entire hydrogen allocation, so the whole star is the core. But the Sun has a...
  33. bornofflame

    [MultiVarCalc] Find the mass of the solid

    Homework Statement Let ##a > 0##. Find the mass of the "solid bowl" consisting of points inside the paraboloid ##z=a(x^2+y^2) \text { for } 0\leq z \leq H \text{. Assume a mass density of } \rho(x, y, z) = z##. Homework Equations ##x^2 + y^2 = z^2## The Attempt at a Solution [/B] mass = ##m...
  34. M

    Critical mass for nuclear fusion

    Hello, can you please confirm this statement "Nuclear fusion does not require a minimum mass to occur (critical mass), which is instead a characteristic limit of fission. So you can make small fusion bombs as much as you want."? Thanks!
  35. Sune Irl

    Calculus 2 - Center of Mass and Pappus Centroid Theorem

    Homework Statement determine the center of mass of a thin plate of density 12 and whose shape is the triangle of vertices (1,0), (0,0), (1,1). Then, using the appropriate pappus theorem, calculate the volume of the solid obtained by rotating this region around the line x = -2. Homework...
  36. K

    I Neutrino Mass: Exploring the Oscillation Phenomenon

    Why is there an assumption that if neutrinos didn't have mass they would move at the speed of light? and how does the fact they oscillate prove they have mass?
  37. A

    I What is zero and infinite effective mass?

    What is effective mass? What is zero and infinite effective mass?
  38. J

    Inertial and Gravitational mass - Assertion Reason

    Homework Statement [/B] Homework EquationsThe Attempt at a Solution I think the two masses , inertial and gravitational are equivalent and because of this fact , the ratio of the two masses is one . The correct option should be 1) . But the answer given is 3) i.e A statement is true and R...
  39. Lucw

    Escape velocity when the rocket's mass is not small compared to the asteroid

    Hello When one calculates the speed of liberation of an object with respect to a star, one takes into account the force exerted by the star on the object. But not the force exerted by the object on the star. For small objects, this is valid. But what is the speed of release of a 1000 kg rocket...
  40. N

    Variation of mean momentum of a nucleon with the mass number....

    Homework Statement How to determine variation of mean momentum of a nucleon with the mass number A of nucleus? Homework Equations R=R_0A^(1/3) The Attempt at a Solution Can't find a solution with elementary approach.
  41. hyunxu

    B Calculating Weight and mass of entire black hole

    Its pretty tough to calculate the entire mass and weight of entire black hole.But how we will give a approximate value? How we will calculate its mass and weight? Could you list some stuffs that caught into the black hole? Has any scientist ever visited a black hole and collected data on it...
  42. M

    B Does Relativistic Mass Affect the Way We Weigh Things?

    Hi everyone. I have some questions related to relativistic mass: Does atoms and molecules are affected by this relativistic effects? and does relativistic mass affects the way we weigh things? What I mean is; (and based on my limited knowledge of Special and General Relativity ) atoms an...
  43. J

    Finding the tension of a rope given the mass of a pulley

    Homework Statement mass of pulley is 8 kg Homework Equations m1a=T m2g-T=m2a The Attempt at a Solution I solved question with neglecting mass of pulley but should I?
  44. HappyFlower

    A solid disk of radius 23.4cm and mass 1.45kg....

    Homework Statement A solid disk of radius 23.4 cm and mass 1.45 kg is spinning at 43.1 radians per second. A solid cylinder of radius 12.1 cm and mass 3.33 kg is not spinning. The cylinder is dropped into the center of the spinning disk. After a short time friction has caused both objects to...
  45. R

    How to calculate critical mass?

    Homework Statement How (or if) I can calculate critical mass with the information I'm given? I have to write a criticality safety evaluation for an assignment. The assignment is about decomissioning a dissolver which was used to recover plutonium. On the contingencies section I need to apply...
  46. R

    I Does dark matter contribute to my body mass?

    No I'm not a particularly big person with a weight issue. Somebody asked me this question and I don't know the answer, but somebody here will. OK, it's now accepted that dark matter is everywhere in the Universe, it tends to clump with regular matter because all matter is subject to gravity...
  47. Robin04

    I Transition between energy and mass

    How well is the transition between energy and mass understood? Energy can turn into matter and matter can turn into energy but what is actually happening between the two states? Imagining that matter just simply appears and disappears under an infinitesimal amount of time feels weird to me.
  48. HappyFlower

    A small mass m hangs from a thing string and can swing....

    Homework Statement a small mass m hangs from a thing string can swing like a pendulum. You attach it above the window of your car as shown in the figure. When the car is at rest the string hangs vertically. What angle does the string make? a) when the car accelerates 1.20m/s^2 b)when the car...
  49. E

    What are the forces on the center of mass?

    Homework Statement [/B] A light rope passes over a light frictionless pulley attached to the ceiling. An object with a large mass is tied to one end and an object with a smaller mass is tied to the other end. Starting from rest the heavier object moves downward and the lighter object moves...
  50. A

    Finding the New Acceleration Given Point Charges

    Homework Statement A point charge q1=15.00μC is held fixed in space. From a horizontal distance of 8.00 cm , a small sphere with mass 4.00×10−3kg and charge q2=+2.00μC is fired toward the fixed charge with an initial speed of 40.0 m/s . Gravity can be neglected. What is the acceleration of the...
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