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. B

    Calculate rest mass given relative speed and kinetic energy?

    The answer is 3.079*10^-26 kg I tried doing E=mc^2 20*10^9*1.602*10^-19=m*(3*10^8)^2 m=3.56*10^-26 kg However when I do E=γmc^2 I get the correct answer. Is the question wrong, because isn't it 20 GeV of kinetic energy, not total energy?
  2. P

    Calculating the mass and price of LPG needed to heat water

    Hello everyone, Homework Statement How many kilograms of lpg will you use if you heat 5 litres of water from 20C to 90C everyday for 30 days and how much will that cost if a 12.5kg cylinder is 1750 Rupees The attempt at a solution To heat 1 liter of water by 1C requires 4.18kJ so you then...
  3. H

    I Any direct evidence of gravitational mass increase?

    Is there any evidence that objects moving increasingly closer to light speed gain gravitational mass, in the sense of attracting surrounding (and not co-moving) masses more strongly, rather than solely possessing the increased inertial mass implied by the greater force necessary to...
  4. Levi Woods

    I How Do I Calculate the Mass of a Planet Using a Simulation?

    I'm having trouble with this simulation I was given by my teacher, any help with how I should go about this?https://www.thephysicsaviary.com/Physics/APPrograms/MassOfPlanet/index.html
  5. S

    B Do Black holes reach a critical mass?

    Are there any theories on Blackholes becoming so massive that the forces generated by the matter within them exceeds the forces compressing them and the tipping point leads to a Big Bang?
  6. Justin71

    Inertial force acceleration (vertical axis)

    Hi, How is the inertial force Fi (acceleration) when the system is vertical. I noted Fi_horizontal=m.a, Ff=mg.μ.cos(Θ) et Fg=mg.sin(Θ) .
  7. Hiero

    Torque about center of mass due to Coriolis force, is it 0?

    It’s essentially a question about cross product identities. I want to analyze a problem in a frame of reference which is rotating with angular velocity ##\vec \Omega## relative to an inertial frame. In this non-inertial frame, we have a rigid body rotating with constant angular velocity ##\vec...
  8. jybe

    Mass launched into the air by a spring

    Homework Statement A child's toy consists of a piece of plastic attached to a spring in the figure below. The spring is compressed against the floor a distance of 2.00 cm, and the toy is released. If the toy has a mass of 117 g and rises to a maximum height of 45.0 cm, estimate the force...
  9. A

    I Calculate mass from time dilation

    Based on the exponential growth of time dilation 0.0 - 1.0 if given the radius of an object how do you calculate the mass of the object? Time dilation is a function of gravity. Which can be thought of as escape velocity from a gravitational field. So if you have to achieve .866 c to escape...
  10. Louis Nardozi

    I What is the mass of all photons emitted in the universe?

    What is the mass of all photons emitted in the universe since the Big Bang?
  11. M

    Find the Mass of the Candy Knowing the Total Mass of the Bags

    [Mentors' note: There's no template because this thread was moved from General Physics. The specification of the problem seems adequate without the template] Hi everyone, I am working through stuff based on the Millikan Oil Drop experiment. There is a question that asks to determine the mass...
  12. T

    Spring and mass with varying force -- what is the change in temperature?

    Homework Statement A system consists of a mass m moving in one dimension and attached to a rigid wall by a spring having stiffness constant ##K##, as shown. The mass is subjected to a constant force ##F##, and is in equilibrium with the surroundings at a temperature ##T##. The partition...
  13. Physics Dad

    Finding an expression for the total mass of a star

    I have made an attempt at the question below and just wanted to check if my thinking was correct or totally wrong. Thank you in advance! 1. Homework Statement In a simple model of a star, the density is described as ρ=ρ0(1-r/R), where R is the stellar radius, and ρ0 is the central density...
  14. Z

    Do Photons Have Mass?

    Does a photon have mass?
  15. J

    Automotive Can the mass flow rate change?

    Hello everyone, Can the mass flow rate of air by a propeller connected to an engine through a small tube change if the rpm of the propeller is increased?
  16. Rahulx084

    Mass Transfer: are both convective mass transfer and eddy diffusion the same?

    I have studied that mass transfer is of two types Molecular mass transfer(diffusion) Eddy diffusion then in later portion of the book I found that there is convective mass transfer too, I wanted to ask if both convective mass transfer and eddy diffusion are same ? I read this equation N_i =...
  17. C

    I Detect Negative Mass Matter: Experiments in Solar System

    How could we detect negative mass matter? The only proposal I've ever heard of is that we could detect there's a cutoff frequency in the gravitational waves we receive, due to attenuation of those lower frequency waves by negative matter. Are there more experiments that could be conducted...
  18. A

    I Negative Mass & White Holes: Does It Create?

    does somebody with a negative mass create a white hole instead of a black hole because of its anti gravity property.
  19. M

    Does amplitude depend on mass in SHM?

    Homework Statement Does amplitude of an oscillating spring with an attached block depend on the block's mass? Assuming the spring has spring constant 'k' and obeys Hooke's law. How would the amplitude of the oscillating spring system be affected if the mass of the block were...
  20. C

    I Explicit computation of mass counter term diagrams

    In most treatments of the mass renormalisation in dim reg, I see sources find the mass counter term by extracting the coefficient of e.g the ##m^2## term accompanied by a pole in epsilon. I know the mass counter term is found by placing an X on diagrams where there is usually a self energy...
  21. E

    Angular momentum conservation and center of mass

    Homework Statement Two bodies with an equal mass of M are attached by a pole with no mass with a length of L. The system is placed on a horizontal table and at first it is at rest. At t=0 a bullet with a mass of m hits the pole, as described in the picture. The collision is completely elastic...
  22. J

    Calculate the acceleration of each mass at the instant the thread snaps

    Homework Statement A piece of lead of mass 1.5 kg is suspended from a light spring. A copper sphere of mass 2.5 kg is suspended by keans of a thread as attatched to the lead. The thread is then burnt. Calculate the acceleration of each mass at the instant the thread snaps Homework Equations...
  23. C

    I Mass counter term is a derivative at tree level?

    I've heard the statement that by computing just the leading-order (tree level) diagrams of a process and then computing the derivative of this result with respect to the mass should correspond to the evaluation of the mass counter term diagrams. Can someone explain why this statement is...
  24. Buckethead

    B Does the mass of an object increase in a gravitational field?

    From a frame of reference outside of a gravitational field, does the mass of an object near a gravitational field increase?
  25. F

    Body rotating about its center of mass

    Hello, As many know, when an external force acts on a rigid body and the force's line of action does not pass through the body's center of mass ##c.m.##, the force will cause the body to both translate and rotate exactly about the ##c.m.##. Otherwise, the body will solely translate without...
  26. F

    I Compute the total stellar mass from a galaxy with Red Giants

    Hello, Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago If the luminosity in the B band (absolute magnitude in B-band is equal to -21.22) is dominated by stars of in the RG branch, with masses ##m \sim 1\,\text{L}_{\odot}## (within ##\sim...
  27. F

    From the original burst, fraction of stellar mass still on the Main Sequence

    <Moderator's note: Moved from a technical forum and thus no template.> Suppose that all stars in this galaxy were born in a single major-merger burst event about 10 Gyr ago. From this original burst, I want to compute the fraction of stellar mass still surviving as stars in the main sequence ...
  28. Shivang kohlii

    Amplitude of a mass joined to a spring in the presence of an E-field

    Homework Statement A block of mass m having charge q placed on smooth horizontal table and is connected to a wall thorough an unstretched spring of constant k . A horizontal electric field E parallel to spring is switched on. Find the ampliture of the shm by the block. Homework Equations kx=...
  29. Drakkith

    I What factors determine the composition of a planet's atmosphere?

    I'm curious as to how the mass of a body affects the kind of atmosphere it can hold. I know that Earth tends to lose its lightest gases over time, which is one reason why helium doesn't build up in the atmosphere, whereas planets like Saturn and Jupiter have held on to lots and lots of hydrogen...
  30. E

    Mass falling to a scale from a funnel

    Homework Statement A closed funnel is 10 meters above a weighing scale. At t=0 we open the funnel. and 15kg of sand are coming out of it every second. The velocity of the sand when it comes out is 13m/s, directed downwards (towards the scale). At a certain moment the scale displays a value of...
  31. Izzy Levine

    Help please -- Amplitude of a spring - does it change with mass?

    Hello! In some of my college Physics practice problems, amplitude of a spring in Simple Harmonic Motion does not change with mass (for example, when the mass splits in 2 at equilibrium in a horizontal oscillator - see picture). But, in other problems, the Vmax of the oscillator remains constant...
  32. M

    B Moving Center of Mass Collisions

    If I fire an electron and positron bunch both in the same direction away from my experimental accelerator rest frame such that the electron bunch is fired with higher energy towards a "read end" collision with an already fired positron bunch and they collide a short distance away from the...
  33. F

    B Does galaxy formation conserve mass and angular momentum?

    Last week I posted in General Physics some questions about what happens in a collapsing gas cloud, and I was advised that total angular momentum is conserved. I thought of asking for extra clarification here, as that seems really amazing -- I apologize for asking the same thing twice. I use a...
  34. John McAndrew

    Acceleration of mass depends upon K and L of a spring?

    I have a question that appears elementary, but bizarre in its conclusion: A mass ##M## is accelerated by a spring of length ##L##, wave-speed ##v_p##, spring-constant ##K## and a constant force ##F## at the other end. As ##K## increases, the extension of the spring ##dx## decreases as does the...
  35. O

    How Does the Speed of Block B Compare in a Three Mass Atwood Machine?

    In the cable-pulley system shown here, block A is moving upwards at a speed of 5m/s and block C is moving downwards at a speed of 2.5m/s. What is the speed of block B? (See attached picture) This seems easy, I just want to make sure I'm not crazy. If mass B moves downward some distance d...
  36. P

    Finding the mass of a ball and a rod using torque

    Homework Statement There is a diagram of a rod with its center of mass labeled and a ball hanging down from it, attached by a string. Two torques are applied on either side. You are asked to find the mass of the ball and the mass of the rod. Homework Equations Torque = Force * Lever Arm *...
  37. KarlM

    A Dark matter and energy explained by negative mass

    Any thoughts on this paper? https://arxiv.org/abs/1712.07962
  38. ezfzx

    I Reconciling alpha particle mass

    Ugh ... I remember there was a reason ... but forgot what it was. So here's 3 bits of information gathered from dozens of sources, textbooks, official sites: Alpha particles are identical to Helium nuclei. Alpha particle mass = 4.001506 u helium-4 nuclei mass = 4.0026032 u OK, so ... why...
  39. Kenny555

    Mass and spring on an inclined plane

    Homework Statement [/B] I got part A and B but in part c , but how to relate period to the equation in part b which is not similar to the cosine function of S.H.M . So i don't know how to obtain period from the equation PS: In part b ,I use mgsin(theta)=-kx and then divided by m Homework...
  40. Johnnyallen

    I Planet mass vs. orbital period

    I recently read a short summary of Kepler 11 and the Kepler Mission. I understand that the orbital period of a planet is a function of its velocity and distance from the star, and the mass of the star will also factor in. Question: Is the mass of the planet also a factor? In other words, does a...
  41. M

    Creating Reaction Mass with Electron-Positron Pair Production for Rocket Thrust

    Given a large enough energy source (nuclear?)... can I build a rocket that creates its own reaction mass via electron-positron pair production, and then derive thrust by accelerating the charged particles out the back with a magnetic nozzle?
  42. T

    Atwood machine with variable mass

    Homework Statement We have an Atwood machine like the picture below. one side (left) is a bucket full of water which has a hole on the bottom and the water is flowing with rate ##dm/dt = \alpha = const##. The initial mass of bucket with the water is ##m_0##. On the other side (right) we have a...
  43. V

    What is the Importance of Choosing the Correct Endpoint in a Titration?

    Hey, I've been having some trouble with my Lab report. After doing a titration of an unknown diprotic acid we had to find the molar mass of the acid and then find out which acid it is by comparing it to a list of given acids with molar masses. But when I run through the calculations my answer...
  44. ohwilleke

    I How Much Better Will Top and Higgs Mass Measurements Get?

    The ATLAS and CMS experiments at the Large Hadron Collider (LHC) recently released joint annual review papers regarding their measurements of the properties of the top quark and the Higgs boson, including their masses, respectively. The most recent mass measurement of the top quark are 172.51 ±...
  45. bbbl67

    Calculating Solar Mass using peak Doppler shifts

    Homework Statement Imagine two planets orbiting a star with orbits edge-on to the Earth. The peak Doppler shift for each 70 m/s, but one has a period of 7 days and the other has a period of 700 days. The star has a mass of one solar mass. (Assume 1 solar mass equals 2E+30 kg.) Q1: Calculate...
  46. opus

    Atmospheric pressure- where do we get the mass?

    At sea level, we experience an external force pressing down on us at any given time which is equal to about 15 pounds per square inch. Pressure is defined as: ##P = \frac{Force}{Area}## where Force is equal to mass x acceleration. When we say that we experience this 15 pounds per square inch of...
  47. Gregs6799

    What is the formula for calculating the mass of air in a piston?

    Homework Statement Homework Equations pV = (m/Mr)RT (this is the formula given but I got the wrong answer using it) The Attempt at a Solution Mass = PV / RT R = 8.314 P1 x V2 / R x T1 M = 220 x 0.1 / 8.314 x 298 = 788.549kg Mass = 788.549kg P = 440000 V = 0.1 R = 8.314 T = 298...
  48. M

    Find the mass of a block on an inclined pulley

    Homework Statement Block A is traveling down an incline plane of 35 degrees at 2m/s. It's pulling a 4kg block with a pulley and rope. Coefficient of friction is.12. How heavy must block A be ? Homework Equations F=MA F = WsinΦ + μWcosΦ mgh = 1/2 mv^2 + WD to overcome friction Vf^2 = u^2 +...
  49. F

    Homework - A galaxy in the local universe

    Homework Statement I have the following questions as homeworks and I would like to get help. Here's some informations given to help us to answer : Photometry : U=11.60 B=11.16 V=10.20 Redshift : z= 0.00780 Central velocity dispersion : ##\sigma_{v}## = 210 km/s Introduction : The...
  50. F

    Homework - Interparticle distance between galaxies

    Homework Statement [/B] I have the following questions as homeworks and I would like to get help. Question 1) Give the formal expression of the total number density of galaxies. Why is this expressoin problematic in practice? Question 2) In practice one uses a numerical value for the number...
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