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. T

    Calculating Laser Power from Temperature Rise, Time, and Target Mass?

    Hi Everyone! There is a type of CO2 laser cutter power meter on the market (Product link removed) The meter uses a block of black anodized aluminum bonded to the end of basically a mechanical meat thermometer, and has a zero adjustment on the back of the face to set the base temperature to...
  2. G

    Cylinder with Displaced Center of Mass Rolling Down Incline

    Homework Statement A rigid cylinder of radius ##R## and mass ##\mu## has a moment of inertia ##I## around an axis going through the center of mass and parallel to the central axis of the cylinder. The cylinder is homogeneous along its central axis, but not in the radial and angular directions...
  3. Lee Sung Bin

    B Relativistic Physics: Gravitational & Inertial Mass

    In Newtonian mechanics, both gravitational mass and inertial mass is m. This principle is known as the principle of equivalence. However, I heard that in Relativity, gravitational mass is γm instead of m because total energy of the particle is γmc2. But in special relativity, it is widely known...
  4. J

    Calculating Center of Mass in NH3 Molecule

    Homework Statement In the ammonia (NH3) molecule of the figure, the three hydrogen (H) atoms form an equilateral triangle, with the center of the triangle at distance d = 9.40 ✕ 10^−11 m from each hydrogen atom. The nitrogen (N) atom is at the apex of a pyramid, with the three hydrogen atoms...
  5. alexi_b

    Finding the time it takes for two stacked blocks to travel

    Homework Statement The coefficient of static friction is 0.604 between the two blocks shown. The coefficient of kinetic friction between the lower block and the floor is 0.104. Force F causes both blocks to cross a distance of 3.44m, starting from rest. What is the least amount of time in which...
  6. Sushmita

    A particle of mass 'm' is initially in a ground state of 1- D Harmonic oscillator potential V(x)....

    Homework Statement [/B] A particle of mass 'm' is initially in a ground state of 1- D Harmonic oscillator potential V(x) = (1/2) kx2 . If the spring constant of the oscillator is suddenly doubled, then the probability of finding the particle in ground state of new potential will be? (A)...
  7. A

    Fuel cell mass flow rate magnitudes

    Hello, Can you tell me please the mass flow rate of hydrogen and oxygen per unit of area of electrodes in fuel cells? Or if you have information on the mass flow rate of hydrogen and air per volume of fuel cell stack? I understand this may vary, but I am looking for publications or other...
  8. E

    Calculate the mass when not hanging it in dynamometer

    Homework Statement Hello! I have a physics problem that I can't solve. I'm supposed to describe how I can calculate the mass when knowing the µv (I don't know the english term but I'm guessing friction...something (friction when the object is not moving)). You are allowed to use a dynamometer...
  9. J

    I Zero Active Mass in FRW cosmologies

    What do people think of Fulvio Melia's argument for the necessity of "zero active mass" in FRW cosmologies? (i.e. the overall equation of state must be ##\rho+3p=0## at all times) Here is a link to an interesting lecture video: Here is a recent paper: https://arxiv.org/abs/1807.07587
  10. Gregs6799

    The mass of air in the pressurised air tank

    Homework Statement A pressurised air tank supplies compressed air to an air engine. When the air engine is not running the absolute pressure in the tank is 300 bar and the temperature of the air is 60°C. Calculate: (a) The temperature of the air in the high pressure air tank when the air...
  11. H

    I How certain are we about black hole mass density?

    The Wikipedia entry on "White dwarf" has a table listing the densities (in kg/m3) of various objects/substances, and states that an earth-mass black hole has a critical density of 2 x 1030, about 13 orders of magnitude denser than atomic nuclei. Has such an enormous density been calculated...
  12. Leonardo Machado

    I Neutron Stars mass and radii observation data

    Hello everyone. I'm currently working on NS mass relations and trying to plot a curve with predicted masses-radii and observations on NS. There are some free data at this website: http://xtreme.as.arizona.edu/NeutronStars/index.php/neutron-star-radii/ . I downloaded the .tar file and tried to...
  13. babaliaris

    I Is the universe actually just mass and length?

    After reading some classical physics I learned that the entire physics is actually studying the combination of 3 quantities mass, length and time. Anything in the universe is just the combination of mass and length and time. And why i say that? Because if you notice the formulas that the...
  14. S

    I Gravity's Effect on Mass: Exploring Its Impact

    (This is to check my understanding ) I gather that gravity being a space-time distortion is thought to affect everything - mass, radiation, whatever - and can be thought of as an accelerational effect. If it is an acceleration, even entities with mass = 0 are accelerated (?). So is there any...
  15. H

    Mass going up an inclined plane with initial velocity Vo

    1. Vo Mass=m 2.So we tried two ways of doing this, one is by taking the y component of the i itial velocity and using that and the other by using the component of its weight parallel to the initial velocity.They give conflicting answers. For the left one it turns out to be t=Vosinθ/g But for...
  16. S

    B Energy & Momentum of Spacetime w/o Mass

    So the gravitational field has energy and momentum, and so you can never have a spacetime with an energy stress tensor set to 0. Is this like a constant then? that you can calculate for a portion of spacetime with no "stress energy tensor"?
  17. T

    B Brown Dwarf Mass Gain: Does Radius Increase?

    Why wouldn't a brown dwarf grow in radius if it started to gain mass?
  18. AlvisPrabhu

    How are Photons massless? How can a particle have no Mass?

    I did look it up , but couldn't find anything that explains this in a simple manner.
  19. Hasan Delifer

    I Why Does Energy Have Mass? Exploring Quantum Field Theory

    Hey, first of all I apologize if this isn't the right thread because I was confused of where to put this. Recently I've learned about Quantum Field Theory and the Higgs Field. I kind of understand why the Higgs Field gives particles mass. From what I have learned it's because the field is...
  20. T

    Fluid mechanics: Bernoulli's equation and conservation of mass

    Homework Statement A mechanical servo-mechanism comprising of a movable piston-cylinder within a vertical cylinder operates based on a venturi contraction in a horizontal 350mm diameter pipe that delivers a fluid of relative density 0.95. The upper end of the 100mm diameter vertical cylinder is...
  21. P

    Deriving the Equation for Average Water Mass Flow Rate in Water Rocket Launches

    Hey, I'm a student who has to complete a written assignment for physics. I chose to launch water rockets and investigate the effect of volume on the range. I am trying to also come up with a mathematical model however I am struggling to understand an equation I found the following equation to...
  22. M

    I Will Space Expansion Lead to the Formation of Black Holes and Neutron Stars?

    1) space is expanding at an increasing rate, therefore things are getting farther from each other and therefore increasing in velocity. 2) the faster an object moves relative to another, the more mass it has 3) supermassive objects can turn into neutron stars, black holes, etc. Therefore, will...
  23. Krushnaraj Pandya

    The mass of a photon in motion

    Homework Statement Find the mass of photon in motion. Homework Equations E=hf p=hf/c The Attempt at a Solution I just started studying modern physics and am aware of the above two equations. However equating E to 1/2mv^2 gives a different (wrong) answer while equating p to mv gives the...
  24. Rahulx084

    What Is the Concept Behind Finding Mole Fraction in Gas Absorption Problems?

    A gas stream containing 3% A is passed through a packed column to remove 99% of A by absorption in the water . The absorber operates at 25 degree Celsius and 1atm and the gas and liquid rates are to be ##20\frac{mol}{hr ft^2}## and ##100\frac{mol}{hr ft^2}##. Find the ##(NTU)_{OG}## ...
  25. K

    I Standard boost, particles with mass M > 0

    Weinberg considers (p.68 QFT Vol. 1) particles with mass M > 0. The Little Group is SO(3). He wants to calculate the rotation W(Λ,p) ≡ L-1(Λp) Λ L(p). He says that for this we need to choose a standard boost L(p) which carries the four momentum from kμ = (0,0,0,M) to pμ. He then shows the...
  26. S

    Mass of Photon: What's the Proper Explanation?

    I read an internet meme: I was going to respond that photons are "massless" particles, but then I realized that photons have energy, and thus must have mass. What's the proper explanation here?
  27. P

    Finding the mass of a photon with given wavelength

    Hi, stuck on this question, hoping someone could help 1. Homework Statement Two identical photons of wavelength 4.22x16^-7m are created when a certain amount of matter M, is converted into energy, calculate the Mass (M) The Attempt at a Solution E= hf which is hc/wavelength E= 4.71x10^-19J...
  28. Rahulx084

    Various Pressures in mass transfer

    I'm confused between partial pressure, total pressure, boiling point , vapour pressure , saturation pressure and saturation temperature.These things haunt me in my subject mass transfer. I get really confused when this words come in a liquid - vapour system, I cannot identify what these pressure...
  29. J

    MHB Can you calculate the total mass of three parcels at a post office?

    At a post office, there are three parcels of different masses. The mass of the first parcel is y grams. The mass of the second parcel is 500 grams greater than that of the first parcel. The third parcel is 210 grams lighter than the first parcel. a) Find the total mass, in grams, of the three...
  30. I

    Chemistry How to get moles from MO having % of mass?

    Homework Statement This is a question from a chemistry book Two oxides of a metal contain 27.6% and 30% of oxygen respectively. If the formula of the first oxide is MO, find that of the second? 3. The Attempt at a Solution In the first MO, if the total amount is 100g, then O is 27.6g...
  31. M

    Continuity equation and mass flowing through two pipes

    Can we apply continuity equation between the given two cases? The only difference in the second case is that the pipe of diameter d2 is replaced by a pipe of diameter d3. Will the mass flow rate be same for both the cases.
  32. S

    Finding the acceleration of the center of mass

    Homework Statement Two forces F1 →= 2i ^ + 3j^N acting on a mass m1 =1.5 kg, andF2→= i^+ j^N acting on a mass m2= 1.0 kg.The magnitude of the acceleration of the center of mass of the system is?
  33. L

    I A question about invariant mass

    A question of invariable mass. In a inertial system, the invariable mass of a system never change with time. This system may not be an isolated system. Whether in any inertial system, the invariant mass of the system remains unchanged.Or, in a certain inertial system, what is the necessary and...
  34. MARX

    Kleppner:Mechanisc: 7.33 Grooved cone and mass

    Homework Statement A cone of height h and base radius R is free to rotate around a fixed vertical axis. It has a thin groove cut in its surface. The cone is set rotating freely with angular speed ω0, and a small block of massm is released in the top of the frictionless groove and allowed to...
  35. M

    Problem about a rigid body pulled by a mass

    Homework Statement A solid body consisting in two concentric disks of masses m1, m2 and radius r1<r2 is linked through a ideal rope to a mass m which falls down with a certain acceleration. The solid body moves of pure rolling. Find the acceleration a of the mass. Homework Equations P-T=m*a...
  36. HCverma

    How to get atoms of something having % of mass?

    Homework Statement Two oxides of a metal contain 27.6% and 30% of oxygen respectively. If the formula of the first oxide is MO, find that of the second? Now my problem is how to find the atoms of O from the masses of 27.6% and 30.0 %? Homework EquationsThe Attempt at a Solution I can see that...
  37. caitphys

    Circular orbit change after gaining mass ejected from sun

    Homework Statement A satellite of mass m is in a circular orbit of radius R about a star of mass M. The star ejects 1% of its mass by means of a spherically symmetric wind which removes the mass to a large distance. What are the new nearest and furthest distances of the satellite’s orbit around...
  38. HCverma

    12 amu and 1.9924 X 10^-23g express the mass of a atom of C?

    Homework Statement 12 amu and 1.9924 X 10^-23g express the mass of an atom of C? Homework EquationsThe Attempt at a Solution Do 12 amu and 1.9924 X 10^-23g express the mass of an atom of C? As I know, 6.023 X 10^23 atoms of C weighs 12 g, 1 atom of C weighs 1 X 12 / 6.023 X 10^23 = 12 amu...
  39. HCverma

    What does it mean by 1 amu? The mass of a proton?

    What does it mean by 1 amu? the mass of a proton or a neutron or an electron? If the mass of O is 16 amu, then what makes 16 amu in O atom? 16 protons or 16 neutrons or 16 electrons?
  40. F

    Experiments about impact of mass in different areas

    There's important experiments showing the equivalence of inertial mass and gravitational mass ( the Eotvos experiments), but I couldn't really find many that show the equivalence of mass (or the stress-energy tensor) in other contexts. These are some of the variants of mass I'm interested in...
  41. G

    A Charged particles mass before symmetry breaking

    How could electrically charged particles be massless before the symmetry breaking? Wouldn't the energy stored in the electric field contribute to particles mass?
  42. T

    B Why don't high mass stars expand and cool?

    When a high mass star starts to fuse heavier elements, the core heats up the outer layers enough to for them to begin fusion of their own. My question is: because the star hasn't gained any mass, but it has increased in temperature a lot, why doesn't the star expand and cool like a red giant...
  43. HCverma

    Is AMU the unit for both 'atomic mass' and 'molecular mass'?

    Is 'AMU' the unit for both 'atomic mass' and 'molecular mass'?
  44. HCverma

    Does 'molar mass' include an atomic weight for single atom?

    Does molar mass include an atomic weight for single atom and molecular weight for molecules?
  45. S

    Rod w/ Pivot and Attached Mass Pendulum

    Homework Statement A solid rod of length L and mass M has a pivot through its center and is originally horizontal. Another mass 2M is then attached firmly to one end of the rod, and released. What is the maximum speed of the mass 2M attained thereafter? (Cornell 2009) Homework Equations Not...
  46. Y

    I Effective electron mass of tungsten

    Hello! Please tell me what Effective electron mass of tungsten and Effective hole mass of tungsten?
  47. S

    Centre of mass of a hollow pyramid

    Question: Calculate the centre of mass of a uniform, square-based pyramid of height H and base length B (taking the centre of the base as the origin). Hence, or otherwise, derive an expression for the centre of mass of such a pyramid with a pyramid-shaped hollow cavity (of height h and base...
  48. R

    B Universe's Flatness: Mass, Gravity, Dark Energy Explained

    So, this is a bit of an odd question, but something I was curious about. I recently learned in layman's terms that the universe is considered flat because of how we measure triangles in 3D space, in particular the CMB. I've also learned that the cosmological constant that was derived from GR...
  49. S

    I Specifically, why is the neutron heavier than the proton?

    Proton is made of 2 up, 1 down quarks Neutron is made of 2 down, 1 up quarks The up and down quark have different masses, which account for some of the mass difference. I've also read that hadron masses depend upon the interactions/dynamics inside the particle, not just the quarks contained...
  50. Sebastiaan

    I Calculating Robert Zubrin's Dipole Drive Mass Flow

    I'm trying to understand calculation made Robert Zubrin in his presentation on Dipole Drive source: In here he made the following statement "A Coulomb of protons has a mass of 0.011 milligrams. If the jet power is 400 W, and the potential difference is 64 V, so the proton current will be...
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