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. Anmol Dubey

    Finding time taken to stop a skater given mass, velocity and force

    I derived the formula for t but don't know how it works Δt = p/F I got p = mv = 60*8 = 480kgms-1 Δt = 480/120N = 4s Is that correct?
  2. A

    Find the center of mass of a uniform semicircular plate of radius R

    $$rcm = \frac{1}{M}\int_0^\pi(rdm)$$ $$dm = \sigma{dA}$$ $$dA = (\pi*R^2)*\frac{d\theta}{2\pi}$$ $$\sigma = \frac{M}{\frac{\pi*R^2}{2}}$$ $$dm = M*\frac{d\theta}{\pi}$$ $$r = R(cos(\theta)\vec i + sin(\theta)\vec j)$$ $$rcm = \int_0^\pi{\frac{R}{\pi}(cos(\theta)\vec i + sin(\theta)\vec j)} =...
  3. ergospherical

    I Effective mass in terms of electron states

    I'm trying to figure out the second order extension of the "trick" used on page 92 (https://www.damtp.cam.ac.uk/user/tong/aqm/solid3.pdf) for the calculation of the effective mass matrix ##m^{\star}_{ij} = \hbar^2 (\partial^2 E/ \partial k_i \partial k_j)^{-1}## on page 94. I think for this one...
  4. Barbequeman

    Consider three models of the Mass distribution in the Milky Way

    I attached a Jpeg with my attempted solution but I´m not sure if I´m on the right way... I hope for a correction in my calculations
  5. Oldman too

    I A new concept in Low Mass Dark Matter detection

    Summary:We propose a search for low mass dark matter particles through momentum recoils caused by their scattering from trapped, nanometer-scale objects. The Paper linked details a novel concept for detecting WIMPs. I hope to see more work performed on the idea in the future...
  6. BranRubaba

    I EM waves have no mass but they do have momentum?

    I was studying radiation and came across an article: https://www.wtamu.edu/~cbaird/sq/2014/04/01/light-has-no-mass-so-it-also-has-no-energy-according-to-einstein-but-how-can-sunlight-warm-the-earth-without-energy/#:~:text=In summary, all objects with,not the only massless object. Which said...
  7. O

    Engineering Mass flow rate as a function of time

    At first, I inputted h(t), of which I solved for, into the mass flow rate formula. So it looked something like this, m-dot(t) = -(density)*[sqrt(g*(H-(g*d^4*t^2/D^4)]*(pi/4)*d^2 But I don't think that's right? Any thoughts?
  8. V

    Trouble with a Rocket Propulsion question (Variable Mass & Momentum)

    I chose to set the upwards direction to be positive and dM/dt = R = 190 kg/s, so I can solve the problem in variable form and plug in. With the only external force being gravity, this gives M(t) * dv/dt = -M(t) * g + v_rel * R where M(t) is the remaining mass of the rocket. Rearranging this...
  9. P

    Physics homework help needed -- A mass sliding down a ramp with friction

    When mass M is at the position shown, it is sliding down the inclined part of a slide at a speed of 2.19 m/s. The mass stops a distance S2 = 2.1 m along the level part of the slide. The distance S1 = 1.18 m and the angle θ = 28.10°. Calculate the coefficient of kinetic friction for the mass on...
  10. A

    I Why doesn't the released mass m2 on pulley have higher acceleration?

    Consider the pulley in the attached image to be frictionless. (a) If m2 is released, what will its acceleration be? My question is why wouldn't m2's acceleration be greater if released rather than attached to the string because m2 released is no longer subject to the string's upward force tension?
  11. Ranku

    I Axion Mass Acquisition: Do Axions Acquire Mass?

    Do axions acquire mass the same way as other particles, through the Higgs mechanism?
  12. A

    I Mass of Backpack in Moving Elevator

    A backpack is attached to a spring scale which is attached to the ceiling of an elevator. The elevator is moving downwards with an acceleration of 3.8 m/s^2. The scale reads 60 N (Fscale). What is the mass of the backpack? The solution to this problem says that Fscale - w (weight) = Fnet. This...
  13. T

    B Understanding Nuclear Fusion and Particle Interactions

    What is the precise mechanism by which matter is converted to energy?
  14. P

    Acceleration of Mass m: Problem Solving

    The problem that i am facing has to do with acceleration. The problem states that we have two balls with the same mass m that stands on two different tables. Between these balls are a wire with the length 2l, which i assume means 2 * l, where l is a value i choose. In the middle of the wire (x =...
  15. rudransh verma

    B Understanding Weight and Inertia: A Comparison of Mars and Earth

    https://www.feynmanlectures.caltech.edu/I_09.html “Weight and inertia are proportional, and on the earth’s surface are often taken to be numerically equal, which causes a certain confusion to the student. On Mars, weights would be different but the amount of force needed to overcome inertia...
  16. rudransh verma

    A mass sliding down the inclined plane -- Will it stop?

    For lower half ,$$Fnet=-\mu F_N+mg\sin \phi$$ For upper half, $$v^2=u^2+2as$$ (s is half of the total slant distance) $$v^2=0+2\frac{mg\sin \phi}ms$$ $$v=\sqrt{2g\sin \phi s}$$ again for lower half, $$v^2=u^2+2as$$ $$0=2g\sin \phi s+2\frac{-\mu F_N+mg\sin \phi}ms$$ $$\mu=\frac{2gm\sin...
  17. M

    Finding the mass of two metals in an alloy

    I looked for solutions on the internet but all of them had given mass and looked for volume , but that isn't given here. I tried something like subtracting the two weights or trying to find mass from the weight but i can't find the correct awnser
  18. L

    Newton's Cradle same diameter, different mass

    Ball drops cm P (Momentum) Metal 10cm 92.4 Marble 10cm 29.4 Ball drops cm KE Metal KE 10cm 64.68 Marble KE 10cm 20.58
  19. Darrencc

    B Does Gaining Weight Affect Mass?

    Hello, I am teaching eleven year olds about gravity. There is no issue about this subject, however I would like someone to help with a model answer. As mass never changes. What is the best answer when I am asked that if someone gets 'fatter', do they not put on mass? Thanks in advance.
  20. T

    I Pole mass and non stationary mass of a particle

    Is the pole mass of the particle it's characteristic mass? When particle physicists calculate the mass of elementary particles, like top quark, do they mean the pole mass? If not what makes the apparent mass of a particle different from pole mass?
  21. Dario

    B Where does the mass of a W boson come from in beta decay?

    During beta decay an electron and neutrino are emitted at very high speeds. I thought that the electron and neutrino were the product of w boson decay but I recently learned w bosons are over 80 GeV worth of energy. My question is, where does this mass come from? I know that atoms get enough...
  22. F

    Hot air balloon mass including increase in mass with balloon volume

    Hi guys, M can then be split up into 2 components: the mass of the payload which is known, and the mass of the wing. The wing material has a known thickness and density meaning its mass is given by: surface area of wing* mass per m^2 (mass m^2 is used as density and thickness are known so an...
  23. A

    Max Angle of Mass on Incline Surface

    Hello, I've worked through the free-body diagram to compute the answer: tan(𝜃) = 0.67 𝜃 = arctan(0.67) = 33.822... The answer is supposed to be approximately 42. Yet, tan(42) is not 0.67, is the suggested answer wrong?
  24. D

    Need help with spring mass oscillator and its period

    I thought I would multiply b to the whole equation of T, but I have no idea how to formulate into the type of solution it wants
  25. I

    B Calculate needed dimensions of table - Center of mass, levers etc

    My high school physics days are long ago ;) This is not homework, well, other than it is work, at home. For a real application: Very space constrained "workshop", got a bench drill press, and want to build a table on wheels for it, to be able to move it into a corner when not needed. Those...
  26. S

    Inverse square law of gravitation and force between two spheres

    I recently encountered this problem on a test where the solution for the above problem was given as follows: $$F= \frac{Gm_1m_2} {r^2} $$ (1) but $$ m=\frac{4}{3}\pi R^3 $$ substituting in equation (1) $$F= \frac{{G(\frac{4}{3}\pi R^3\rho})^2 }{2R^2} $$ where r=radii of the two spheres m=mass...
  27. snoopies622

    I Seeking the Equation of Motion for a charged mass attached to a spring

    I'm surprised that this question only occurred to me recently. If a have an electrically charged mass attached to a spring and set it oscillating, the resulting production of electromagnetic waves must cause a kind of "friction", a force resisting the motion of the charged mass, so that its...
  28. M

    B What happens to the Core of a main sequence star as additional mass is added?

    So there is a post going around the facebook groups about what would happen if we could pour a Sun sized bucket of water onto the sun, the claim being that the sun would gain mass and become a bigger, hotter burning blue star. I know this cannot happen but I was just curious as to what would...
  29. runningphysics

    Two masses connected by a rope on a pulley on a ramp

    I have no clue how to do the problem. I created a free body diagram for each block. I assume that it is simpler than I am making it out to be.
  30. R3ap3r42

    Invariant mass and energy balance

    a) Two particles have energies E1 and E2, and momenta p1 and p2. Write down an expression for the invariant mass of this two-particle system. Leave your answer in terms of E1 and E2, and p1 and p2. b) A typical photon (γ) in the Cosmic Microwave Background (CMB) has an energy of kBTCMB, where...
  31. W

    Thermal Physics Problem -- Dropping a hot mass of iron into 20C water

    Hi, The solution for this question is thermal energy lost= thermal energy gained 0.200x450x(300-T)=1.0x4200x(T-20) T=26 degrees celcius. However, I am struggling to grasp why (300-T) is used. I have always known a change in something to be final - initial. Therefore change in T= Final-...
  32. J

    Why isn't the scaling factor included when stating particle mass in eV?

    not technically a homework question, just figured it fit here.
  33. R

    Mass, acceleration and velocity

    Good Evening All, I have an assignment i am struggling with really hope you can help. The question reads Describe how force, momentum, Angular momentum, kinetic and potential energy are linked with respect to mass, acceleration and velocity I know the following Force – the push or pull...
  34. R

    SOS -- Questions about mass, acceleration and velocity

    Please some one help! I am about to go stir crazy. I am really struggling to answer a the following question...describe how force, momentum, Angular momentum, kinetic and potential energy are linked with respect to mass, acceleration and velocity. Its probably really easy but science is not my...
  35. S

    Shift in position of plank when a man moves on it (Centre of mass)

    Lets take the original position of the man to be our origin The plank is uniform so we can assume its mass to be concentrated at its center i.e. 4m from the origin Xcom= m1x1+m2x2/m1+m2 =50(0) +150(4) /50+150 =3m There is no external force on the system so the centre of mass does not move...
  36. S

    Finding the frequency of a string based on Mass and Tension

    I saw the following problem in a test I was reviewing: I don't understand how they got their answer. I used the formula: ƒ=sqrt(T / u) / 2L where f is the frequency of the string, T is the tension, u is the linear mass density, and L is the length of the string. I got: T = mg = 50 * 9.8 = 490N...
  37. S

    Calculate Mass of Satellite: Step-by-Step Guide

    I am not really sure what to do to find the mass of satellite. Equation for orbital speed: $$m \frac{v^2}{r}=G\frac{m_1 . m_2}{r^2}$$ $$v_{orbital}=\sqrt{\frac{GM}{r}}$$ Equation for escape speed: $$KE_1+GPE_1=KE_2+GPE_2$$ I tried to take position 1 as the position where the satellite orbits...
  38. hutchphd

    B Exploring Relativistic Mass & Length to Help STEM Students

    Comments please Is there good sobriquet to use for relativistic length ? Just a thought to aid the struggling college frosh STEM students
  39. M

    Stargazing Understanding the Chandrasekhar Mass Units for Relativistic Lane Emden Equations

    Using Lane Emden and n = 3 (relativistic), I calculate the correct mass -- the Chandrasekhar mass (about 1.4 Msun) The equation goes Mtotal ∝ a3, because at n=3, the density, ρ, cancels out. a2 ∝ K/G = Kg2 → a3 ∝ Kg3. Here K ∝ h c or Kg m3/sec2 and G ∝ m3/Kg/sec2 This implies the mass, Mtotal...
  40. duchuy

    Determine the velocity of a particle in mass spectrometry

    Hi, I am trying to determine the velocity of the particle with the mass m coming out of the acclerator. I tried writing : Ep(i) + Ec(i) = Ep(f) + Ec(f) Ec(f) = Ec(i) - Ec(f) But at this step, I'm no longer sure how to express Ep with V because : In my textbook, it's written : Ep = 0,5...
  41. J

    How many atoms are in a given mass of metal?

    Hi all, This may be simple chemistry, but I haven’t engaged this topic for a very long time. I have an experiment where I need to measure the masses of some elemental (99%pure) metal cubes and I also want to know how many atoms of each element there are within them. From memory, Avogadro’s...
  42. A

    B Newton's second law of motion -- Why is it F=m*a and not F=m+a?

    Why F=m*a i.e product or multiplication and not F=m+a? i.e addition or summation?
  43. Lunct

    B Gravitational Force acting on a massless body

    It's a well known fact that acceleration due to gravity is independent of the mass of the accelerating body, and only depends on the mass of the body it is accelerating towards and the distance from it. One can prove this mathematically very easily. F=GMm/r^2 (equation 1) but also F=ma...
  44. physicsneedslabs

    Finding Spring Constant When Given Amplitude, Time, and Mass

    I averaged the masses and times (which i took the time given and divided by 10 because in the problem it says you measure the time it takes to complete 10 oscillations) then plugged them directly into the T=(2(pi)((m/k)^1/2) and got the wrong answer. This is really confusing me because I don't...
  45. E

    Calculate Deflection for Aluminium Tube Beam - Inertia, Mass & δ

    Hi There, I am wanting to calculate the amount of deflection (δ) from a simply supported Beam. My Beam is an Aluminium Tube ø30mm with a 3mm Wall Thickness. Force (F) - 500N Length (L) - 610mm Youngs Modulus (E) - 68 Gpa Moment of Inertia (I) - ? δ = F L³ ∕ 48 E I Q1: Is this the correct...
  46. A

    Coolant Mass Flow Rate Through Subchannel in Nuclear Fuel Assembly

    I am trying to find the mass flow rate of coolant through a channel within a hexagonal nuclear fuel assembly. I am given the specific heat of the fluid, the coolant inlet and outlet temperatures, the total power produced by a single fuel pin, the diameter of the fuel pin, the length of the fuel...
  47. B

    Chemistry Does anhydrous compound Penta-hydrate have mono- or tetra-hydrate forms?

  48. A

    Engineering Motion equation and transfer function of mass on a conveyor

    Denote wheel turning angle as theta--> Induced EFM (Em)=Kb*Theta_dot. Voltages on the wheel: R*i= V - Em Moments on engine's axis: Kt*i-C*a + a (m+M)*x_double_dot=0 (As Jm negligible). From here I would find another equation to have x and theta expressing each other, but i think I'm...
  49. T

    Chemistry Calculate molar concentration of 500 cm^3 glucose solution with mass part 5%

    .
  50. L

    B Space propulsion without mass ejecting

    When the pulse is given at A, the box move to the right. When it is absorbed at B, the box stop.
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