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. 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...
  2. 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...
  3. 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...
  4. ayans2495

    Hiking the Appalachian Trail: A Beginner's Guide

  5. 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...
  6. 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...
  7. 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##
  8. Paige_Turner

    B Why Does Mass Pull on Other Stuff?

    Why doesn't it repel things... or just pass through and leave distance unchanged?
  9. 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...
  10. 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.
  11. 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...
  12. 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...
  13. 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?
  14. 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...
  15. 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...
  16. Rikudo

    A mass collides with an inclined plane

    In my textbook, it is stated that "if an object elastically hit an frictionless inclined surface with angle between the vector of initial velocity and an imaginary line that is perpendicular to the surface ##\alpha##,then the angle between the line and final velocity vector will also be...
  17. G

    B Can there be time without mass?

    According to Relativity, any object traveling at c will not experience time, because of time dilatation. It will seem to the object that it has traveled instantly while ages may pass outside. Further, an object without rest mass will always travel at c. Therefore, if there were no objects with a...
  18. M

    A New string formulae for Higgs mass and cosmological constant

    https://arxiv.org/abs/2106.04622 Calculating the Higgs Mass in String Theory Steven Abel, Keith R. Dienes [Submitted on 8 Jun 2021] There are at least two properties of the Higgs mass one might hope to explain with such a fundamental calculation: its criticality, and its participation in...
  19. Ang09

    Moment of Inertia with varying distance from Centre of Mass

    h = d1 + 0.08 d1 = h - 0.08 d2 = h + 0.08 I of the vertical portion = 1/12 m (l^2 + b^2) + md1^2 = 1/12 m (0.28^2 + 0.04^2) + m(h - 0.08)^2 I of the horizontal portion = 1/12 m (l^2 + b^2) + md2^2 = 1/12 m (0.28^2 + 0.04^2) + m(h + 0.08)^2 The moment of inertia for the whole T-shape about...
  20. V

    B I have a conceptual question about relative mass

    If mass increases with velocity(v), can I say velocity is a quantity dependent on (v)? m=Ymo, m>mo so why can't we say that the mass (matter) increases and yes what increases is the energy to make your speed keep increasing?
  21. D

    PEX Pipe in Residential Subfloor Thermal Mass

    Hello friends! We are installing a future provision for a Rocket Mass-type woodstove in our home. This is a future project but realized that we could take advantage of the open area between the footing and finished floor by adding an insulated block of concrete with PEX pipes for Heating and...
  22. S

    I Special Theory of Relativity & Conservation of Mass

    Does the law of conservation of mass fail to meet the first postulate of the special theory of relativity(the laws of physics are the same in all inertial frames of reference)?
  23. T

    Relationship between material mass and weight

    What does it mean that the relationship between material mass and weight is constant and proportional? Hi! Yes, another question... I have many doubts. :) I hope someone can help me with this apparently very basic doubt, but I feel like a stupid monkey trying to join two sticks to reach bananas...
  24. qnt200

    I If energy is relative, is the rest mass also relative?

    The mass (rest mass) of an atom, for example, depends on the kinetic and potential energy of the particles and their individual masses. Kinetic and potential energy are relative. Why is the mass not relative, but the same for all reference frames?
  25. R

    Get the mass of an argon atom and its molecular weight from Cv

    I don't see how isolate m or M. That is, how to get rid of <v^2> which is how I wrote the average of v2
  26. momoneedsphysicshelp

    How do mass and radius affect gravitational pull on planets?

    Can someone please verify if my reasoning is accurate? I chose E) Planets B and D because they both have the same ratio of mass to radius which is the lowest of all the other planet options. Due to the fact that they have mass and radius evened out the gravitational pull will pull weight down...
  27. C

    I Rate of Time/Mass: Is There a Constant?

    Is there a constant for the rate at which time slows relative to the amount of mass? If so would there be a base measure eg time being present with 0 mass
  28. A

    I Is mass the source of spacetime?

    Mass curves the spacetime. In electrodynamics, an electron curves an electric field (if there is one) - because it has an electric field of its own. The electron is the source of an electric field(maxwell equations) Is there an analogy to space-time, is mass the source of the space-time field as...
  29. snypehype46

    I Mass spectrum of open bosonic strings

    I'm learning string theory from the book by Zwiebach and others. I'm trying to understand the quantisation of the open string and its mass spectrum. In light-cone gauge the mass-shell condition of an open string is given by: $$M^2 = 2(N - 1)/l_s^2$$ where ##N =...
  30. F

    Pulley system -- Calculate the mass that balances this pulley system

    I've been stuck at this pulley system for a while. I've calculated the force of which A pulls => FA = sin25*50*9.82 = 208.5 N But I get stuck on the free body diagram. Can someone help and explain the freebody diagram
  31. dedocta

    I Mass, Distance & Early Universe: Is It Mere Coincidence?

    I was playing around with a theory that dark matter was behind the opaque wall of the early universe, as gravity would not be opaque. Not sure if the numbers fit yet, but one odd thing I calculated was the distance squared of 46 billion light years, as the mass of the early universe, by time...
  32. ayans2495

    Balancing Nuclear Equations: Mass & Atomic Number Confusion

    I don't understand, in balancing a nuclear equation, the sum of all the mass numbers and atomic numbers, given on the upper left and lower left side of the element symbol, respectively, must be equal for both sides of the equation. So why does the sum on the left side equal to 20, but the sum on...
  33. CyanPowder

    Calculate the Mass of Ice cubes needed to cool a soft drink

    Summary:: TLDR : Drink cooled from 17 C to 7 C with either ice cubes (method 1) or soapstone stones (method 2). Calculate the mass of each item that would be needed to cool the same drink. Given the information provided. In order to cool a drink (“cola” for example) from a storage-room...
  34. L

    Mass vs Mass as a Force (Weight)

    Been thinking about mass today and came up with a question. Why is that objects on this Earth describe its weight in Kg, g, mg, Mg? IE 2.2Lbs is 1Kg. So why do we name the 1Kg to be mass, but the 2.2Lbs we call weight. Both have to be a unit of force if there is a conversion factor between the...
  35. Max2020

    Engineering Work and energy -- Change in KE due to a force F acting on a mass

  36. H

    Calculate the block mass in an equilibrium system with two supports

    The attachment is the key. I wonder where the (3/8)L comes from. Can someone explain it, please? Thanks.
  37. Domuks

    How do I find average kinetic energy if I don't have mass of the gas?

    So always in my problems i had mass (M) but now i don't and it seems impossible to solve this problem if I don't have mass I think i am missing something. I was looking for similar problems in my book and internet and didn't find any.
  38. Drakkith

    B Mass and Surface Gravity of a Dyson Sphere

    I'm re-watching Star Trek TNG and I just started the episode where they encounter Scotty aboard a ship that's crashed into a Dyson sphere. That got me thinking. What would the mass and external surface gravity of a Dyson Sphere be? I've done the math myself, but I'd appreciate someone double...
  39. K

    Calculate the charge to mass ratio in this mass spectrometer problem

    2(7.28E+08) / (0.038^2) R^2 i don't know how to get r
  40. V

    Ideal Vs Real Mass Pulley system

    Below is an ideal mass pulley system that we encounter in many problems under Newton's Second Law of Motion questions. Its supposed to be massless and frictionless i.e. string slips over the pulley and pulley does not rotate. In a real system, the pulley is assumed to be massless, whereas in...
  41. S

    MHB Forces of 8N: Find Angle & Mass of Particle

    Two forces each of size 8N, have a resultant of 13N. a) Find the angle between the forces b) The two given forces of magnitude 8N act on a particle of mass m kg, which remains at rest on a horizontal surface with no friction. The normal contact force between the surface and the particle has...
  42. M

    Is acceleration still equal in the presence of air resistance?

    I remember being told that heavier things fall at the same rate as lighter things when everything else is equal. But this guy does a demonstration of a Xenon balloon falling faster than a Neon balloon. Why? Also an overloaded plane may not be able to fly, but it has the same aero dynamics, it...
  43. AN630078

    Graphs of s, v and a for a mass with a piece of paper attached

    I understand that velocity is defined as the rate of change of position or the rate of displacement; and that acceleration is defined as the rate of change of velocity (it is the derivative of velocity). Morever, I believe I know that for SHM these graphs vary sinusoidally (I have attached a...
  44. J

    B Experimental evidence for effective mass increasing with speed

    What is the best recent experimental evidence for effective mass increase (momentum/velocity) with speed, with experimental details? Searching the web all I find is either very old ones (early 1900s). Or vague generalized statements like (Wikipedia) "Many additional experiments concerning the...
  45. J

    Harmonic motion - Find the Mass held between two Springs

    So first I find the energy using the eqn (1/2)kA^2. Since there are two springs with the same k I multiply it by two to get kA^2. Energy I get is 2.0475, Now I use E=(1/2)m(wA)^2 to find mass. Again since there are two springs I use E=m(wA)^2. m=E/(wA)^2. w=(2(pi))/T btw. I get the answer of...
  46. yucheng

    Where is the equilibrium point of a mass sliding down slacking cord?

    My two questions: The author claims that ##T_1=T_2## and ##\alpha = \beta##, and this is supposed to be clear the force triangle. Why is this so? Is it possible to use calculus of variation to find the lowest point C? That is, by maximizing the triangle ABC (Area of ABC = ##\frac{1}{2}(line...
  47. T

    Question about the role of mass in inclined planes

    Hi! I have a question about inclined planes. In the diagram I attached, you can see that, with or without friction, mass does not affect the acceleration of the block. However, in my experience, the more people I put on my sled, the faster it goes. Why is this?
  48. P

    Does Raising My Arm Change the Center of Mass?

    Let me imagine myself standing on the Earth with my arm in the resting position perpendicular to the ground. Now if I decide to raise my right arm by 90 degrees, now that it is parallel to the ground. I have shifted my center of mass in this process. But the center of mass will not accelerate...
  49. George26

    Conservation of mass: control volume approach question

    Summary:: Control volume question that has a brine solution entering a tank and mass accumulates over time. Hello, I'm currently struggling with a control volume approach question that has a brine solution entering a tank. I get to a point where I have a first order differential equation. I...
  50. H

    Calculating Pressure & Mass for Hydrogen Tank Filling

    As I stated in the summary I'd like to calculate the required pressure and mass of a tank of hydrogen that would allow me to fill a second tank with 10kg of H2 at 700bar. I am trying to get an idea of the feasibility of doing this, putting aside, for now, how the primary tank would itself be...
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