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. W

    B Why does Jupiter have a stronger gravitational pull than Earth?

    Objects fall on Earth at 9.8 m/sec² independent of mass. If gravity is independent of mass why does Jupiter pull an object more than the Earth does? Is that inconsistency within the law or in my perception?
  2. Tomer Aman

    B Why Does Matter Fall to Center of a Mass? Explained

    Hi Guys. I have a question about General Relativity. If, according to GR, Mass curves Spacetime and gravity is simply matter falling into that curveture, why does all matter fall equally regardless to their spatial position on the mass. For example, why do people in let's say Australia fall into...
  3. Helena Durrant

    Problem involving friction, with a mass being pulled up a slope

    (The answer from the markscheme is 26.7)
  4. R

    Tension in a rope wrapped around a shaft, pulling in a mass

    Hi everyone, I am thinking of solving it this way. Since Fc=mw^2r. and Fc=T. Then -dT=dmw^2r. where dm=m1(dx/l). and putting the lower at x=l the tension will be T=m2w^2l. Am I doing things right.
  5. Amik

    Velocity of the center of mass of the system

    I believe they are the same?I think i am wrong.
  6. R

    Two movable pulleys lifting a mass

    I solved the last part of the previous question, But I got no idea how to start solving this question Like how the rope is being attached, is it attached to the inner disk or the outer one.
  7. A

    Volume average of mass function

    I want to express <m(x,y,z)> over a sphere of radius R in terms of $$<\rho(x,y,z)>$$ e.g $$<m>=\frac{\int_{sphere R}m(x,y,z)dv}{\int_{sphere}dv}$$ $$<m>=\frac{\int_{sphereR}(\int \rho(x,y,z)dv)dv}{\int_{sphere R}dv}$$
  8. Uberhulk

    Mass of the Earth Traveling at 500,000 mph?

    What would be the mass be of a planet traveling at 500,000 mph - if we assume the planet has the same mass as the Earth i.e. 5.9 sextillion tonnes?
  9. Luke Tan

    Conservation of Energy of the Center of Mass

    In classical mechanics, the energy of a system of particles (say with 2 particles) in an external field is given by $$E=\frac{1}{2}m_1|\vec{v}_1|^2+\frac{1}{2}m_2|\vec{v}_2|^2+V(\vec{r}_1)+V(\vec{r}_2)+V'(|\vec{r}_2-\vec{r}_1|)$$ Where V is the potential energy of the external field, and V' is...
  10. G

    I Antimatter energy from a small amount of mass

    If an object's energy is proportional to its mass, how can a gram of antimatter produce more energy than 80 kilotons of TNT? Where does all this energy come from such a small amount of mass?Skip to 5:19 of the video where he says this: Please explain this in the most simplest way possible.
  11. G

    To find the amplitude of a mass on an elastic string

    Could I please ask for help with the following: It's the final part I am having problems with. So at this point we know we have SHM of amplitude (5/4)L Now, using x = a cos(nt) ----- where we now know that n = sqrt(4g/L) we can find the time at which x has any value. So for exmaple, when...
  12. A

    I Does p=mc Apply To Photons? | A.P. French's Special Relativity

    In A.P. French's Special Relativity, the author said the following, As I understand, photons are massless, so I don't think the last equation above applies to photons, but then, when deriving it, he used an equation proper to photons (##E=pc##). So in which context is ##m=p/c## valid?
  13. A

    I E=mc^2 Mass: Rest Mass m0 vs Relativistic Mass γm0

    Is the mass that appears in E=mc2 the rest mass m0, or the relativistic mass γm0?
  14. rachelmaddiee

    Chemistry Converting the number of atoms to the mass of an element

    Atoms-to-mass conversion Step 1: First, convert the number of atoms to moles, then convert miles to grams Step 2: Second, use the inverse of the Avogadro’s number(moles to number of atoms) Are these the correct steps?
  15. Roundandround

    Unraveling the Mystery of Mass & Force: A 180 lb Person

    Background: My understanding is force and mass are two different things. Mass is how much matter is in a body Force is mass multiplied by an acceleration. Here on earth, that acceleration is 32.2 Ft/s2. Therefore, for the same mass, there can be different forces depending on the...
  16. cemtu

    Classical Mechanics "variable mass" linear motion problem in one dimention.

    Please help please
  17. AL115

    A spool that rotates and slides freely while pulling a mass

    My attempt to solve the first one. T-mg=ma T=m(g+a) TR = Iα I=(1/2)(M)(R^2) α=a/R TR=(1/2)(M)(R^2)(a/R) T=(1/2)Ma mg+ma=1/2Ma a=(2mg)/(M-2m) And... I got a wrong answer. As usual.
  18. Arman777

    I Calculating the Maximum total neutrino mass by using cosmological boun

    In an article its written, $$\Omega_{\nu} = \frac{\rho_{\nu}}{\rho_{crit}}=\frac{\sum m_{i,\nu}n_{i,\nu}}{\rho_{crit}} = \frac{\sum m_{\nu}}{93.14h^2eV}$$ Now I am trying to derive this for myself but I could not. Can someone help me ? So the values are, ##\rho_{crit} = 1.053 75 \times...
  19. rachelmaddiee

    Chemistry Determining Moles and Particles from Mass of a Compound

    mass = 37.2 g AICI3 (given) number of ions = AI3+ Ions (unknown) number of ions = CI- Ions (unknown) mass = g/formula unit AICI3 (unknown) The ratio of AI3+ Ions to CI- Ions is 1:3 Molar Mass AICI3 (1 x 26.98 g/mol AI) + (3 x 35.45 g/mol CI) = 133.33 g/mol AICI3 molar mass = 133.33 g/mol...
  20. S

    Calculating the Mass Flow Rate of a boiler

    Im trying to do some past exam papers. If i can get help with the method on how to solve and have correct formulas, it will help me. I) There is one formula in the notes to get mass flow rate: Heat lost by steam = Heat taken up by water GsHfg = (GwCpw)(change in temp) Gs x 2748 x 10x103 =...
  21. B

    Mass of Gas Ejected: 1.25kg - Is it Reasonable?

    This is the problem below that I have tried doing I ended up getting the mass of gas ejected to be 1.25kg from doing the following Would you say this is a reasonable value to get Thanks in advance!
  22. Ammar2211

    A block of mass m is dropped onto the top of a vertical spring....

    Summary:: A block of mass m is dropped onto the top of a vertical spring whose force constant is k. If the block is released from a height h above the top of the spring, a) what is the maximum energy of the block? b) What is the maximum compression of the spring? c) At what compression is the...
  23. Saptarshi Sarkar

    I Effects of photons having a finite mass

    Few days back, our college professor told us that if a photon were to have a finite mass, then the Coulomb potential between two stationary charges separated by a distance r would be strictly zero beyond some distance. He told us that it was due to the reason that photon is the elementary...
  24. M

    A Does Dim Reg really avoid a photon mass?

    In the loop integral for the one-loop correction to the photon propagator in QED, the dominant term, after Wick rotation and angular averaging, has the form (omitting uninteresting factors) $$(1-2/d) e^2 \eta^{\mu\nu}\int_0^\infty \frac{p^{d+1}}{(p^2+\Delta)^2}dp,$$ where ##p## is the absolute...
  25. V

    Convert Mass Flow Rate to Molar Flow Rate

    how can i convert mass flow rate into molar flow rate using density of the gas.
  26. Saptarshi Sarkar

    A particle of unit mass moves under the action of force F=-k²/x³ ....

    I tried solving the differential equation by integrating both sides wrt t but this does not work out and I am doing something wrong. How do I integrate such an equation properly? d²x/dt² = -k²/x³ => dx/dt = -k²t/x³ => x = -k²t²/2x³ + d
  27. M

    Bernoulli's Equation and water rockets

    So I'm playing around with some water rockets and I'm trying to figure out how fast the exhaust velocity of the water is. I've had an experimental approach using high fps camera to record and analyse (using tracker) the exhaust velocity. I'm using a 0,5 l soda bottle with 0,085 L ; 0,135 ; L...
  28. D

    Getting Force with distance, mass and time

    I'm sorry but I can't even attempt this question since I'm pretty much clueless, I got the notes but I don't understand them.
  29. Arman777

    Calculating the mass of the neutrino for a relativistic case

    I came across a question that states What mass would a neutrino need to still be relativistic today (T = 2.37K) ? So for a particle to be relativistic we need ##pc \gg mc^2## Well Neutrino was relativistic in the early universe, so I took the time when the neutrino decoupled which is...
  30. Petronius

    Determine the mass of the planet using Newton’s Law of Universal Gravitation

    Hello, and thank you again to anyone who can confirm if I have the right answer or who can give me some suggestions. This question felt like a bit of a surprise because we have not yet covered one where the mass of a planet was missing. Thus, my confidence in my work is low. Part b felt like a...
  31. Y

    Power and Mass Question -- A helicopter accelerating and ascending

    I started with calculating the Ep and Ek of the helicopter and got this: Epi = 490m Eki= (1/2)(400m) Epf = 12740m Ekf = (1/2)(1681m) I don't really know where to go from there. Do the unknown mass variables cancel out? I'm lost!
  32. tnibbz

    How to Calculate Invariant Mass for Negligible Particle Mass?

    So I know that since we are ignoring the mass of the electron, and the proton starts at rest, the proton has no KE and the electron has no rest energy. So the initial total energy of the system would be rest energy of proton + KE of electron = 2GeV + .938GeV = 2.938 GeV and since energy is...
  33. G

    Change in Mass of Hurricane Harvey's Rain

    First I have to explain that this is not actually a homework problem. It is a problem I created to use in a sort of game. If I made a mistake, it tends to ball up the game. So I am looking for someone to double check my answer, and to point out any errors in my statement about physics. I prefer...
  34. E

    Rocket moving through a cloud of dust, variable mass problem

    The first way to solve this is to just say, by conservation of momentum, that M_{0}v_{0}=(M_{0}+Apx)\frac{v_0}{2} where Apx is the mass of dust the rocket comes into contact with in a distance x. For the second method, by considering the change of momentum of the dust in 1 second, we know the...
  35. L

    Oscillations of a Block Mass attached to a Spring on an Incline

    Why doesn't the incline angle play a role in changing the ##m## component of this equation? ##T = 2π\sqrt{\frac{m}{k}}## FOR QUESTION 25, PART B: ANSWER:
  36. J

    I Does Dark matter get trapped in black holes and increase their mass?

    Dark matter passes through everything, but is only influenced by gravity, so in the case of a neutron star, since dark matter doesn't interfere with ordinary matter, it can just pass through it, but neutrinos might be stopped by it's density, as neutrinos can just pass through stars almost as if...
  37. T

    How forces act on a shape and its centre of Mass

    Hello all After a lot of support from people like Dr.D, mfig and collinsmark I have finally understood the concept of Centriods and Centre of Mass. I am now trying to understand how a uniformally distributed force and a non uniformally distributed force acts on a shape. If I had an oddly...
  38. G

    Find the height to which a mass rises

    Hi, Could I please ask for help regarding the following question. The book answer H = ( 3 - 3 sqrt(2)/4 ) L (natural length of string is L) Here is my diagram: The green level represents the unstretched string. The blue level is the string and mass in equilibrium. The purple level is the...
  39. T

    Defining the Centroid, Centre of Mass, Centre of Gravity for 2D/3Dshapes

    Homework Statement: Defining Centroid, Centre of Mass, Centre of Gravity for 2D/3Dshapes Homework Equations: Defining Centroid, Centre of Mass, Centre of Gravity for 2D/3Dshapes Hello all; I am trying to understand the terms:- - Centroid for a 2D shape and 3D shape - Centre of Mass for a 2D...
  40. T

    Engineering Help With Mass and Weight Units

    Hello all I was hoping someone could clear up the units & difference between Mass and Weight. I live in the UK. I weighed myself today on the scale and the scale told me that I weighed 95kg. What bothers me is that if:- Mass - Is the amount of "stuff" I am made from which is measured in kg...
  41. G

    Understanding SHM of a Mass: Exploring Energy Conservation and Elasticity

    Could I please ask for views on this question: I've answered the whole thing and agree with the answers given in the textbook. Here are those answers (where Y is the modulus of elasticity of the string = lamda in the question): Period of motion = 2 * PI * sqrt( ma/Y ) Speed passing through...
  42. maistral

    Boundary conditions for convective heat and mass transfer + wall Temperature

    I am operating via finite differences. Say for example, I have this pipe that contains a fluid. I have the boundary condition at x = x1: k is the effective thermal conductivity of the fluid, T is the temperature of the fluid at any point x, hw is the wall heat transfer coefficient, and Tw is...
  43. G

    A Fermion mass terms in Peskin and Schroeder's book

    I'm currently looking at how fermion masses are produced via the Higgs mechanism in "An Introduction to Quantum Field Theory" by Peskin and Schroeder. It all makes a lot of sense and I've been fine with it so far, but I ended up getting stuck on something that's driving me nuts. I feel silly...
  44. U

    Energy Conservation as an explanation for v=0 for spring mass system

    My Solution: For the displacement graph, the gradient is crucial to predict the behaviour of the displacement of the block through time. At 1: System is released - velocity is zero, considering forces acting on block, kx < mg, as block is observed to move downwards, and object is...
  45. bieon

    Exploring the Conservation of Momentum and Energy in a Tarzan Swing Collision

    My Attempt So Far: 1) Drawing a diagram based on the question. Diagram 1: Pendulum Diagram Based On Question 2) List down pieces of information found in the question. θ1=53° θ2=37° m1=m1 m2=m1+50kg vi=0 3) Since 53°+37°=90°, I redraw another diagram making it into a right angle triangle in...
  46. M

    An object with mass m moving on x'x and Ep(x) = (1/2)*k*(x^2 - 4)^2

    Hi ! This is my try: Is that correct ? Thanks
  47. G

    To find the equilibrium position of a mass attached to an elastic string

    Hi, can anyone see if I have made an error in answering this simple question, my answer is not the one given in the textbook. Here's my diagram of the system in equilibrium. So the mass has dropped a distance x below the midpoint of PQ: So the forces balance as: T1 = g + T2 So, using...
  48. F

    Inverted pendulum -- What force is applied at the center of mass?

    Summary: I know that in order to keep inverted pendulum balanced when it leans forward, I should accelerate the bottom of it, but what is the force which is applied to center of mass of the pendulum with balances torque due to gravity? Is it inertial force? We assume that our inverted pendulum...
  49. F

    How Does Eddington Luminosity Limit Black Hole Mass Accretion Rates?

    The Eddington luminosity gives a limit on the mass accretion rate of the black hole and therefore of the mass of the black hole. L_edd = 13*10^38 M/M_sun [erg s-1]. When I calculate from this I get that the maximum mass is M = 10^(-8)M_sun... which is impossible. Any ideas?
  50. Ranku

    I Dark Matter Mass: Evidence of Low-Mass?

    Is there any indication, such as through gravitational lensing, that dark matter has a low-mass compared to visible matter?
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