Mass Definition and 1000 Threads

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. J

    Equation of motion of a mass on a 2d curve

    So ##T+U=\frac{1}{2}m(\dot{x}^{2}+\dot{y}^{2})-mgy=constant##. If I derive this with respect to ##t## $$\dot{x}\ddot{x}+\dot{y}\ddot{y}-g\dot{y}=0$$ Then I use ##\dot{y}=\dot{x}\frac{dy}{dx},\ddot{y}=\ddot{x}\frac{dy}{dx}+\dot{x}^{2}\frac{d^{2}y}{dx^{2}}## to get...
  2. H

    Finding the coefficient of kinetic friction - problem with a mass on a plane

    I don't really know how to begin this problem. I need some advice
  3. E

    Where Is the Center of Mass of a Leg?

    The center of mass of someone's thigh, shank, and foot are located at the following coordinates: Thigh: (2.7, 3.2) Shank: (2.1, 2.5) Foot: (1.5, 1.9) If the masses of them are respectively 9.6, 2.9, and 0.9 kg, where is the location of the entire leg? ANSWER: CM = (2.5, 3)I'm having trouble...
  4. G

    Calculation of minimum angular velocity of a mass on a spinning plate

    Problem Statement: How to calculate minumum angular velocity of a mass on a spinning plate Relevant Equations: f=mrw^2 Hi, here's the question: a) A rough horizontal plate rotates with a constant angular velocity of w about a fixed vertical axis. A particle of mass m lies on the plate at a...
  5. J

    Mass compressing an unattached spring

    How far will the spring extend, given that the block is not attached? Will it extend beyond its natural length? How to calculate at what point the box comes off the spring?
  6. S

    Spring is stretched, then attached to a mass, what is its speed at x?

    Dear all, I am back with another Spring problem. I have tried to use the insights I gained from your help last time: https://www.physicsforums.com/threads/find-v-x-of-a-mass-suspended-from-a-spring.972942/page-3#post-6190934 I figured I start with calculating the new equilibrium by ## x...
  7. Lunct

    B Can virtual particles have an imaginary mass?

    I was talking to a physicist who said to me that virtual particles can have a mass of a constant times by i ,as in the root of -1. I have been thinking about this more and it intrigues me. I have done some research into this and can't find further details. If they have an imaginary mass does...
  8. B

    B The Physics of a Black Hole Merger: What Happens to Mass?

    What would happen if a black hole made entirely from anti-matter merges with another black hole made from normal matter? Since most of the product left over from the annihilation is in the form of light (gamma rays) would the black hole lose mass?
  9. T

    B The Term "no mass" is poorly defined

    Problem Statement: NA Relevant Equations: NA Come across the mentioning that some particles have "no mass". Is this stated by physicists because there simply isn't evidence to prove that they have mass. It doesn't seem logical to make a fact based on absence of information to the contrary...
  10. brotherbobby

    Center of gravity and over-hanging blocks

    The red dots show the CM of each block. ##x## is the amount by which the upper block overhangs the lower block. The blue (dashed) line shows the CM of the combination. For maximum overhanging, this line lies on the edge of the table below. By symmetry, the CM lies exactly midway between the two...
  11. J

    I Mass for solving the nuclear energy level

    Hi all, I'm trying to solve a problem of finite square well for the ##s## states graphically. The task is to find energy levels and wavefunctions of proton in a spherically symmetric potential, first for deuteron then ##^{48}Ca##. What makes me confused is the mass. For deuteron, the mass used...
  12. B

    Mass transfer coefficient from a numerical model

    Dear all, For an assignment, I am trying to find the relationship between the Sherwood number and the Reynolds number in a channel for different laminar velocity profiles, where there is a concentration of a species at both the top and bottom wall which is transported to the fluid. For this, I...
  13. e2m2a

    Center of mass momentum of a photon and electron system

    Suppose there is a photon with momtum p=h/lambda moving in the positive x-direction. Suppose it collides with an electron at rest and is completely absorbed by the electron, and that after the collision, the electron moves to the right with the same momentum of the photon. This seems...
  14. I

    Sound waves carrying mass and how to measure it

    I don't know in which category this subject belongs to. Anyways, here it is: https://www.sciencealert.com/a-new-study-backs-up-claims-that-sound-waves-really-do-have-mass-after-all?fbclid=IwAR2Cmsxm_Garm0PVn03f4UxVQ8adcK4Il3A_N7bUbJT1KaGR1ZfCbGuWVLE How exactly is this measured? Can we expect...
  15. PeterDonis

    I Gravitational Mass of a Ball of Photons: Concept Q10.4 in Gen Relativity

    This is based on "Concept Question 10.4" in Andrew Hamilton's General Relativity, Black Holes, and Cosmology. I have modified the question somewhat in order to focus on what seem to me to be the key issues. Suppose we have a spherically symmetric ball of stress-energy surrounded by vacuum. More...
  16. W

    Does Newton's Second Law for Torque Work for the Centre of Mass of an Object?

    I am reading Tipler & Mosca 5th edition. On pages 289-290 there is an example problem which seems to assume that Newton's second law for torque works just as well when we apply it to the centre of mass of an object. However, before this example problem was introduced, the authors did not state...
  17. C

    I Accelerator Particles: Speed of Light & Mass Increase

    In an accelerator when you're pushing/pulling a charged particle with a field that travels at the speed of light why should we expect to the particle to exceed the speed of light.
  18. W

    I Variable mass F=ma versus Rocket F=ma

    In the book by Tipler & Mosca, the section on F=ma for variable mass derives the following equation: ##\mathbf{F}_{ext}+\frac{dM}{dt} \mathbf{v}_{rel}=M\frac{d\mathbf{v}}{dt}## where ##\mathbf{F}_ext## is the external force on the system as a whole (ie not just the variable mass sub-system...
  19. O

    What is the final speed of a mass collision?

    I am stuck, please help. I did the conservation part but then i can't move on.
  20. S

    Find the charge of a mass hanging from a pendulum in an electric field

    Hi, so I was able to solve this problem by just equating the forces (Tension, mg, and EQ). But I thought I could also solve this problem with Conservation of Energy. However, I calculated it several times, and I never get the right answer this way. Doesn't the Electric Field do the work to put...
  21. nuuskur

    Effects of velocity on weight (mass?)

    A ballistics-esque question. Suppose we are driving at ##x \text{ m/s}## and we have to suddenly brake. For students in driving schools they are told something along the lines of "during the braking, the body experiences ##y \text{ kg}## of force" or "the mass of the body is much higher than at...
  22. S

    A Gravity on Planets: Does Mass Affect Free Fall?

    My current understanding is that a person falling toward the surface of a planet with no atmosphere, would feel no force acting upon themselves even though they are accelerating relative to the planet. If the mass of the planet suddenly tripled while the person is in free fall, would the person...
  23. W

    I Centre of mass of a semicircle using polar coordinates

    I am labelling this as undergraduate because I got it from an undergraduate physics book (Tipler and Mosca). The uniform semicircle has radius R and mass M. I am getting the wrong answer but I can't see where I am going wrong. Any help would be appreciated. My solution: The centre of mass...
  24. zonde

    I Binding Mass Distribution in Gravitating Bodies

    For bound system to form it must radiate away binding energy. By mass energy equivalence mass of the bound system is reduced proportionally to amount of binding energy. The question is from which mass this "binding mass" is subtracted. Common answer that I have seen is that this binding mass is...
  25. wasmaro

    How much mass is released to decrease the pressure

    My best estimate was to find the water height and assume it remains constant when venting the air. I know the initial weights of vapor and liquid ( I know the total mass of substance inside the vessel), so I find the new density of water and vapor and calculate the "new" mass and take the...
  26. Error404!

    A Effective Mass of Electron for White Tin

    For some work of mine i need the plasma resonance frequency for tin nanoparticle, i searched various research papers and found different efffective masses tin for different orbits. here i attached screen shot from W A Roger and S B Woods (Cyclotron effective masses in white tin). What value is...
  27. wasmaro

    [Thermodynamics] How much mass is extracted to decrease pressure

    I have a feeling some integration will be required, I just want to see if anyone know of a quick way.
  28. K

    Finding the average water mass flow rate in a water rocket

    Could anyone kindly kind me as to where this formula is derived from and how, because I searched and can't find it anywhere
  29. K

    MATLAB Spring mass impact system in Matlab - How to correct it?

    I am new to Simulink and I wanted to start practicing using a spring mass damper system. My first tutorial was this: Later, I wanted to model a spring system where a mass moving at a known velocity hits the spring. The governing equation and a similar modeling method given in the previous...
  30. J

    B Atom's mass -- does it change with energy levels?

    Summary: Does an atom in an excited state have a higher mass than when in its ground state? Summary: Does an atom in an excited state have a higher mass than when in its ground state? Does an atom in an excited state have a higher mass than when in its ground state?
  31. IonReactor

    I Role of mass and quantum gravitational effects in friction?

    Friction is commonly thought to arise from the electromagnetic forces of the atoms at the boundary between two surfaces in contact. However it occurs to me that, in addition to charge quanta, there are also mass quanta present in this system and they could very well play a role. Now, I'm just...
  32. M

    B Rest Energy and a 1 million solar mass black hole

    Suppose there is a 1 million solar mass black hole. A 1.022MeV photon near a nucleus produces an electron-positron pair a distance=A from the event horizon. The positron’s vector is directly “up” away from the singularity. It doesn’t have escape velocity. It reaches an apogee at distance=B from...
  33. L

    B How does the Higgs field “Give mass”?

    Problem Statement: How does the Higgs field “give mass” Relevant Equations: The exact way that particles interact with the Higgs field and therefore create mass. I’m trying to figure out how the Higgs field works, one problem is that while I originally though of the Higgs field like a medium...
  34. Lifeboatboy

    Elementary Q: how to calculate speed of Mass B, upon impacting Mass A

  35. M

    A Verifications of running charge / running mass

    Hi everyone, I understand that the phenomenon of running charge predicted by QFT has been experimentally verified: the physical charge on an electron really does vary with the energy at which it is measured. I have two questions: (1) Does anyone know what the canonical experiments confirming...
  36. S

    Find v(x) of a mass suspended from a spring

    Hi all, I have a problem that I've been grappling with for the past 2 hours. I was confident at first that I found the correct solution, but when I tried to verify I didn't have a constant in my v(x) function. Here is my attempt: I appreciate your help kind internet strangers!
  37. K

    How to find the deceleration of a mass colliding on a spring?

    Problem Statement: A known mass at a know velocity collides on a spring of known stiffness. What is the equation that governs the deceleration of the mass, so that the force on the spring could be found? Relevant Equations: 1/2 m*V^2 = 1/2*k*x^2 + 1/2*m*(Vo)^2 Kinetic energy of mass before...
  38. H

    Spring on a mass that is held back

    Hi. I have a question regarding the above image and want to know whether I am right or not. In the image there is a body with mass m and in the middle of the body there is a spring. The body is pulled upwards and then it hits two fixed rods such that the body cannot move upwards any more. Now...
  39. H

    I Measuring Mass of a Bowling Ball Dropped into a Black Hole

    In a recent thread we discussed the idea that an object slowly dropped into a black hole, can have its rest mass recovered, as energy, if slowly brought to a halt at the event horizon. Once the object is dropped, it would be unrecoverable, and the BH would gain no new mass. I am under the...
  40. MatNX

    B What ways are there for something to lose mass?

    How can san object lose mass? You can use Antimatter or Fission or Fusion to turn it into energy. Also, one can just cut a piece of the object off. But are there any other ways to remove matter from an object? (Feasable and theoretical)
  41. T

    Finding out the mass of gas transferred outside of a room

    I thought I should use the ideal gas law to find out moles of air that would be transferred out through the window but the temperature and volume outside is not known. Can you help me further? thanks
  42. A

    Calculate the mass defect of a carbon-12 nucleus

    My attempt: Proton 1.00728ux6+ Neutron 1.00866ux6=12.09564u 12.09564u-11.9967u=0.09894u E=mc^2 E=0.09894x(3.00x10^8ms-^1)^2
  43. N

    A Is energy inversely proportional to mass?

    Hello. I'm a graduate student in electrical engineering, and I'm taking a class in semiconductor physics. My professor has used this equation for the energy of an electron in a semiconductor: $$E=\frac{\hbar^2 k^2}{2m^*}$$ This seems to imply that energy is inversely proportional to mass, i.e...
  44. Buzz Bloom

    I Question regarding the nature of mass inside a black hole

    I was reading another thread which has been closed, so I cannot ask this question there. The question is about a post by @PeterDonis (post #21). https://www.physicsforums.com/threads/what-happens-to-the-inertia-of-a-mass-falling-into-a-black-hole.970627/ There are no internal pressures inside a...
  45. S

    Classical Book about center of mass frame of reference and fictitious force

    Hello I have learned about conservation of momentum, Newton's law (1st, 2nd, 3rd law + free body diagram), conservation of energy and finding center of mass of several 2 D and 3 D shapes (non - calculus method). I watched youtube video about two objects connected by horizontal spring and in...
  46. R

    Center of Mass of acceleration and velocity

    I don't understand what I am supposed to do. I know how to find the acceleration of the system, but I am not sure how to find the com acceleration. My guess would be something along the lines of xcom = (m1a1*x + m2a2*x)/(m1a1 +m2a2). Then do the same for the y axis. Then to find the velocity all...
  47. Z

    Vibrations: A momentum impulse starts a mass into oscillatory motion

    The fig. 1.1(a) is a mass m attached to a spring that is fixed to a wall. I don't understand what does "a sudden momentum impulse" means. Is it an external force o what? I imagined that the new equation of motion would be md^2x/dt^2+dp1/dt-kx=0 md^2x/dt^2+mdv1/dt-kx=0 is this the equation i...
  48. arcTomato

    I Please teach me about the mass of Sgr A*

    Hello I have no idea why underline part of my pic says like that. "Radio observations show that the component of this motion perpendicular to the Galactic plane is at most 0.4 ± 0.9 km s−1" So What? Why this sentence shows the mass?? ("The radio emitting source(underline part)" = Sgr...
  49. A

    Estimating the mass of our galaxy, and the number of stars in our galaxy

    A previous thread outlined the problem with a correct answer, however I don't understand where they got the formulas from. Here are the steps I've taken so far: 1. Convert 2*10^8 years to seconds = 6.3072*10^15 seconds (period,T) 2. The previous thread then went on to say you plug period and...
  50. P

    What are the steps for calculating the center of mass of this object?

    What are the steps to calculating the center of mass for this object? I don't want a numerical answer just the theory. I understand I need to calculate COM for all axis, we know in the Y axis it's dead centre because of symmetry but I don't know how to do it for the others. A hint would be...
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