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. 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...
  2. 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...
  3. 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 +...
  4. 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...
  5. 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...
  6. H

    Is the mass of the electron constant?

    If the mass of the electron has been changing during the evolution of the universe, then the orbits of the electrons would also change, which will shift the light spectrum of each atom. Could this explain red shift of far galaxies, and the shift is not because the universe is expanding? Henry
  7. sams

    A How to calculate Saturn's mass from Kepler's third law?

    This is not a homework. In Chapter 8: Central-Force Motion, in the Classical Dynamics of Particles and Systems book by Thornton and Marion, Fifth Edition, page 325, Problem 8-19, we are asked to calculate the mass of the planet Saturn. In the instructor's solution manual, the solution for this...
  8. Dorian

    Solid Disk Pulley + 2 Mass system, v derivation using 2 methods

    Homework Statement [please see attached photo] Homework Equations [please see attached photo] The Attempt at a Solution [please see attached photo] The issue for me starts with (but probably doesn't end with) replicating the velocity equation using the Conservation of Energy equations. Is...
  9. SavannahN

    Do I need to consider mass in the equations?

    Homework Statement a. At launch a rocket ship has a mass M. When it is launched from rest, it takes a time interval t1 to reach speed v1; at t = t2, its speed is v2. What is the average acceleration of the rocket (i) from the start to t1 and (ii) between t1 and t2? For now, I am taking...
  10. S

    Center of mass and rotation question

    Homework Statement A 100 g ball and a 250 g ball are connected by a 34-cm-long, massless, rigid rod. The balls rotate about their center of mass at 150 rpm . Homework EquationsThe Attempt at a Solution I solved by first getting the center of mass, then converting rpm into m/s I treated rigid...
  11. Arman777

    I Reduced mass for ##m_1## larger than ##m_2##

    Reduced mass can be defined as ##μ= \frac {m_1m_2} {m_1+m_2}## For ##m_1>>m_2##, ##μ_2≈m_2## How can we prove this ?
  12. shk

    Calculate the mass of a star and a planet that orbits it

    I have problem with an A2 physics question: A planet is orbiting a star at an average distance of 10^9 km. The period of its orbit is 500 Earth days. The gravitational constant is 6.67x10^-11 Nm^2kg^2. a) Calculation the mass of the star. b)Explain why you cannot determine the mass of the...
  13. Urs Schreiber

    A Reference for Hadron mass & spin problem?

    I am looking for articles or books that would clearly and succinctly state the open problem of and issues with computing hadron masses and spins in QCD from first principles, preferably in relation to the open problem of confinement and the general open problem of non-perturbative QCD. Any...
  14. S

    Relativistic Mass Exam Question

    1. Homework Equations E=mc^2 Relativistic mass equation given in the question The first part of the question: I understand 200 MeV is the energy lost as it initially moves with 200MeV however is brought to rest and thus this total kinetic energy must have been transferred from the 'two...
  15. M

    I Modern Definition of Mass: Does a Photon Have It?

    If a photon does the 4 things listed below, why do we say it doesn’t have mass? I guess I’m asking if there’s a clear definition of mass. follows geodesics in spacetime (classically: accelerated in a grav field), curves spacetime (classically: creates a gravitational field), has momentum /...
  16. thebosonbreaker

    Resolving forces: Mass on a string

    Homework Statement A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3N which makes an angle of 30° with the horizontal. Find the angle that the string makes with the vertical and the tension in the string. Homework Equations Body is in...
  17. N

    A The Mystery of Mass: Exploring Electron Inertial & Heavy Mass

    In Abraham Pais book (which was first published in 1982), he states the following: "Quantum field theory has taught us that particles nevertheless have structure, arising from quantum fluctuations. Recently, unified field theories have taught us that the mass of the electron is certainly not...
  18. mfb

    I Measurement of Earth's mass - with neutrinos

    At very high energies Earth absorbs a relevant fraction of neutrinos passing through it. Experiments receive more of these neutrinos from above than from below and the difference depends on the mass of Earth. So why not measure it? Neutrino tomography of Earth The uncertainty is very large, of...
  19. E

    Finding z component of center of mass of a complex shape

    Homework Statement The rigidly connected unit consists of a 2.5-kg circular disk, a 2.8-kg round shaft, and a 4.2-kg square plate. Determine the z-coordinate of the mass center of the unit.Homework Equations ∑zm/∑m The Attempt at a Solution Circular disk: mass = 2.5 kg z = 0 zm = 0 Round...
  20. snoopies622

    B Does Negative Mass Have Physical Significance in Modern Theories?

    Yesterday I wrote a simple computer simulation for a spring which, when released, sends two masses flying in opposite directions, and views the event from two different reference frames. My goal was just to convince myself that relativistic mechanics is self-consistent and indeed every time I...
  21. J

    MHB Mass of weight to keep gate closed

    Hi All, Cannot seem to figure out the question below. I`ve attached an image of the question. I basically need to find the mass of the weight W. The hinged gate will open when the water height is 12ft. The gate is a 5ft wide L shaped gate, hinged at point A. I`ve gone down the line of CW =...
  22. DLeuPel

    I How can I calculate the energy of a body of mass?

    Since E = mc2 the if I know the mass and the energy I can figure out the constant c2, but how do I know how much energy does the body have ? How do I calculate it ?
  23. StillLearningToronto

    Astronomy- Initial Mass Function problem

    1. Homework Statement The Initial Mass Function (IMF) defines the distribution of stellar masses created in a star-forming event. The probability P(m)dm of forming a star with a mass between m and m + dm is given by P(m)dm = km−α dm where α is the exponent of the power law and k is a constant...
  24. F

    Why Do Moments Balance in a Faraday Disk but Not the Forces?

    Hi to everybody! Please: can you help with this problem? A conductive disk with a radius a = 20 cm, with negligible moment of inertia, rotates around its horizontal axis. The disc region around the radius is inserted in a magnetic field B = 0.75 T perpendicular to the disk itself. A mass is...
  25. E

    B What would the universe be like with less mass and energy?

    So I have sort of a conceptual question about the big bang and gravity. Imagine yourself in a universe, in which existed about the number of particles/energy in a 3X3 metre room at any given moment. This universe has the same laws of physics, constants and is identical in every way to our...
  26. R

    Finding the mass of a block attached to a spring

    Homework Statement What is the mass of the block? Given: friction less surface, velocity at each marked point, distance between points 1 and 2, spring constant l = 7 N/m Homework Equations F=ma Kinematic equations The Attempt at a Solution I tried to solve for a in m = F/a in order to find...
  27. A

    Finding Momentum when giving the mass and height

    A 50.0-kg male dancer leaps 0.32 m high. (a) With what momentum does he reach the ground? I know that to find momentum the equation is P = mv, but I only have the mass and distance. I have tried finding the time (D = 1/2at^2) and later used that time to find the velocity (v = d/t). I later used...
  28. M

    Trying to understand the entropy of different situations....

    I just read a book by nuclear physicist Carlo Rovelli on the subject of "Time" and he says that 'entropy' is the only non-reversible process in the basic equations of physics, and he believes time and entropy are related (if I understand him correctly). So this started me thinking on entropy...
  29. S

    Finding mass of unbalanced meter stick from torque

    Homework Statement Unbalanced meter stick has hanging mass of 100g at 0m point. I then moved fulcrum to balance it and it was balanced at the 0.33m point. (The hanging mass and 0m point is on left side) I want to get the mass of the portion of the meter stick on right side, but I am confused as...
  30. K

    How do masses affect the acceleration of the center of mass?

    Homework Statement The vector position of a 4.00 g particle moving in the xy plane varies in time according to 1 = (3i+3j)t +2jt^2 where t is in seconds and is in centimeters. At the same time, the vector position of a 5.95 g particle varies as 2 = 3î − 2ît^2 − 6ĵt. Determine the acceleration...
  31. A

    How to solve for the distance traveled given force, mass and speed

    Homework Statement A car has a mass of 1500kg. If the driver applies the breaks, the maximum amount of friction force that can be applies without skidding is 7000N. If the car is traveling at 25m/s, what is the shortest distance the car can stop safely? Homework Equations I'm assuming it has...
  32. A

    MCNPX - How calculate Kerma (kinetic energy released per unit mass) in Air?

    Hi, my name is alexander, i am student from Institute of radioprotection and dosimetry (IRD). My project is calculate MGD (mean glandular dose) from womans with augmented breast. i am having dificulties to calculate Kerma in air with mcnpx. I drew a block of air above the breast, i am using the...
  33. W

    Centripetal Lab- finding the mass from the slope

    Homework Statement The lab: Centripetal Force Lab a Rubber stopper is moving in a horizontal circle at a constant radius and it is attached to a string where at the bottom, there is a mass where the mass is 100g, 150g, 200g, 250, and 300g (can see image attached) from the lab, I collected...
  34. I

    I Calculating the Mass of a Piston for a Spring-Based Launcher

    I am trying to teach myself Physics, so I can use it in engineering for my own devices. The project I am working on right now is a very simple spring based launcher. This is frustrating me to no end. Here is my objective. I want to lunch a golf ball about 10 or so feet. I know that I need to...
  35. M

    I Measured Isotope Masses: Exploring the Mass Excess

    Has anyone listed the actual experimentally measured masses of isotopes ? I find only the mass excesses listed. Why?
  36. G

    What is the physical significance of A and B in mass spring SHM solutions?

    Hi community, I've been looking at solutions for mass spring shm (undamped for now) ie that x = Acoswt and x = Bcoswt work as solutions for dx2/dt2 = -(k/m)x and that the general solution is the sum of these that with a trig identity can be written as x = C Cos(wt - φ) where C is...
  37. M

    A Renormalized Mass: What is Physically Going On?

    Hello! I am reading Schwarz QFT and I reached the mass renormalization part. So he introduces, after renormalization, a physical mass, defined as the pole of the renormalized propagator, and a renormalized mass which can be the physical mass, but can also take other values, depending on the...
  38. S

    Determine the mass of an object using the angle in the system

    <Moderator's note: Moved from another forum and thus no template.> I have a project from my Mechanics class which consist on building the system on the picture. It has a spring, cable and a protractor. I have to do an approximation of the mass and weight of the object that is put in the...
  39. M

    Oscillating horizontal mass attached to a spring with Friction

    Homework Statement The question is similar to last week’s, except that we will consider how friction may damp the oscillation with time. A block with mass m shown in the drawing is acted on by a spring with spring constant k. The block is pulled distance [x[/0] from equilibrium position (x=0)...
  40. A

    Finding Force by using the coefficient of friction and mass

    Homework Statement A man pushes a 50 kg box up a 20-degree ramp at constant velocity. If the pushing force is parallel to the ramp, and the coefficient of friction is 0.4, how much force is he pushing with? Homework Equations u=Fs, max/Fn Not sure if this equation is needed. The Attempt at a...
  41. J

    Variable mass beans falling on a platform

    Homework Statement A spigot pours beans onto a scale platform. At a time t = 0.0 sec, the spigot is opened and beans begins to pour out (with initial velocity 0) at a rate of 1.00 kg/sec onto the platform from a height of 10.0 m above. (a) At t = 10.0 sec, what is the weight of beans on the...
  42. I

    I How do I convert mass units in physics?

    I am enrolled in a course related with physics, and we have a table of equivalencies of units to get the right units of frequencies. Stiffness Mass Frequency tonf/m ton.s^2/m rad/s kN/m ton rad/s N/m kg rad/s kgf/m...
  43. K

    Max. acceleration of a pendulum changes with its length and mass?

    Hi, If I find out the tangential force on the bob at position 1, it turns out to be m*g*sinθ. From this if I find out acceleration by dividing this equation by m, I get only g*sinθ. Does it mean the max acceleration of pendulum has got nothing to do with its length or mass but theta?
  44. Dukon

    What motor/payload mass ratio -> payload spins the motor

    Given an unconstrained (suspended without contact to anything) electric motor with its own power in total has mass m1 Given the motor shaft is connected to a payload of mass m2 If m1>m2 then: m1 no-spin + m2 spin If m2>m1 then: m1 spin + m2 no-spin What happens at the unit ratio (m1/m2 = 1...
  45. S

    What is the relationship between tension and mass in a system with friction?

    Homework Statement In the figure above a block of mass m is connected to a block of mass M > m by a string. Both blocks sit on a smooth surface with a coefficient of kinetic friction µk between either block and the surface. In figure a), a force of magnitude F (large enough to cause both blocks...
  46. BadgerBadger92

    I Understanding Light, Mass & Higgs Field: Exploring Object Behaviour

    What happens to an object when you negate the Higgs field to give an object zero mass? Does it behave like light and travel instantly without force (or is there a gap here?) I heard if you took away mass from something like a baseball it would just float. How does this reconcile with the...
  47. Krushnaraj Pandya

    Variation in mass and binding energy in nuclear reactions

    Homework Statement I'm perpetually confused keeping track of the energetics of a nuclear reaction and I broke down my conceptual questions into the following parts statement a-In a fission reaction, the two medium sized daughter nuclei each have more binding energy per nucleon than the original...
  48. N

    A What is the dust-to-gas ratio in oxygen-poor galaxies?

    Hello, Assuming that dust is formed by silicates with Mg and Fe. What is the largest possible silicate dust-to-gas ratio in mass?
  49. M

    I The Potential: Harnessing Energy to Create Mass and Possibly Universes

    As I understand E=m*c^2 you can create mass from energy In my imagination that means, that if you create a high enough energy density, then you will create mass equvilant to that energy. (with some loss i imagine) That understanding have made me think, could we, in theory, create enough energy...
  50. jha192001

    Elongation of a spring in a two mass system

    The Question is posted as a photograph with a. little change. One of the mass in the photo is equal to '2m' rather than 'm'. Now the block won't stop consecutively. How would we approach the question?
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