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. A

    Modal mass and kinetic energy in FEM modal analysis

    So, I use Ansys (well known FEM software) and get the next output for a modal analysis toy problem (If you happen to know Ansys that's a pre, but I promise it shouldn't matter). The problem is a simple beam, clamped at one end. I used 160 20-node brick elements to solve it (so no Timoshenko...
  2. cosmologyscience

    I Orbital Velocities and Mass Distribution in Galaxies

    Has anyone looked into the details of stellar orbital speeds and required (visible) mass distribution in the Milky Way? Doing some math here - if the local mass density is significantly higher in the inner 10-15% of the galaxy, and then lower and gradually thinning outwards in the disk, we will...
  3. Bastion

    B Experimental evidence for effective mass increasing with speed

    I am new to this forum and in line with its rules I am trying not to repeat a question already asked. I find that Jeremyfiennes original question I.e Experimental evidence for effective mass increasing with speed” is the question I want to ask but I am not satisfied with the answers given so...
  4. Y

    Friction problem in HS physics -- Mass moving on an inclined plane

    This is a homework problem of my grand daughter. The question is to find out the conditions of an object M on a slope with angle shown and applied force "F". I find there are 3 conditions, sliding up, sliding down and not moving. This is my work. I just want to get comments on my work: At the...
  5. C

    I Do objects of differing mass fall at the same rate in a magnetic field?

    Gravity isn't a force in the strictest sense of the word, yet magnetism is exactly that: a force. As is strong, EW, etc. Therefore, it's possible that the more massive magnetic object gets drawn to the center of a magnetic source at a faster rate than the less massive magnetic object. Discuss!
  6. O

    I F= - mg - kv ? (forces of gravity and friction on a mass)

    Hi I'm just a student so this: F = - mg - kv (Being kv friction) doesn't sound intuitive. Looks like both are going in the same direction... I just don't get it. But that's what my book says (Symon mechanics) and my classmates are also using "-"kv . Can someone explain me please? Shouldn't...
  7. J

    I The Wavefunction when Mass is Much Greater than Planck's Constant

    I understand that the uncertainty is low when you're dealing with a "macro" scale area that is much bigger than Planck's constant. But what's confusing to me is when you know with extreme precision the location, but there's so many particles involved that there is little uncertainty since the...
  8. Rikudo

    How Does the Sign of ##dm## Affect Rocket Propulsion Calculations?

    I have a question. If we assume that ##dm## is positive, is the answer supposed to be different from the one when we regard the ##dm## as negative? 1. If I assume that ##dm## is positive: By using momentum conservation, we will get $$mv=(m-dm)(v+dv)+dm (v-u)$$ simplify the equation $$m \,dv=dm...
  9. M

    B High Frequency Photons: More Mass, More Bend?

    Since high frequency photons have more relativistic mass, should we expect them to bend more than lower frequency lights when traveling through a gravitational field, thus produce a rainbow effect? But we don't seem to experience rainbow effects with star light.
  10. A

    B Gravitational Potential Energy & Mass Change: Andrew's Question

    If I start with two, otherwise isolated, masses M and m initially together and do work to separate them then the work done, I assume, goes into the gravitational binding energy between them. Will the system of mass M and m have increased in mass due to this in accordance with e=mc^2? I...
  11. sachin

    Motion of center of mass under gravity

    While solving this question I could not figure out the concept of two blocks sticking together. the question is, Two particles A and B of masses 1 kg and 2 kg respectively are projected in the directions shown in figure with speed uA =200m/s and uB =50m/s. Initially they were 90m apart. They...
  12. E

    B Displacement of Hanging Mass - Simple Pulley System

    I'm having some kind of mental block. If I extend ##l_x## by ##\delta## ,I expect the hanging mass to move ##\frac{ \delta}{2}##. I can't figure out how this is the case from the constraint: $$ l_x+l_1=C $$ ##C## is an arbitrary length I keep getting that ##l_1## changes by ##\delta##, but...
  13. RealityMechanics

    Determining Reverse Mass Flow Rate Formula for Multiple Diameter Tubes

    Alright, this is more of a conceptual question than a HW question that will nonetheless help me design something. In the attached image, air is flowing through a large area tube and then a small area tube from right to left. A collaborator previously figured out the equation for measuring the...
  14. P

    B Exploring Mass, Gravity & SpaceTime: Ask for Expertise Here

    Greetings. I registered to this forum because of a particular issue regarding Gravity. I'm no astrophysicist or mathematician, i searched to find an answer, but the terminology and equations are a little much for me. I feel the best direct way is to ask people with the right expertise. It is...
  15. Ranku

    I Particle Size & Mass: Same Size Different Mass?

    Are there examples of particles with same size but different masses?
  16. link223

    Oscillation with 2 springs attached to a mass

    How in the world I am supposed to start with this problem? No clue, so can't provide HW solution by any means. regards.
  17. link223

    Analyzing Mass A's Direction of Motion

    I am not very sure how I would be approach this. Obviously it is stated in which direction it's going where we see that mass A goes to the right, but how do I determine this stuff analytically.
  18. pandatime

    Centre of mass (composite rod) - length and densities provided

    I feel like I'm missing something fundamental here. Given only the lengths and the densities, how am I supposed to find a numerical centre of mass?Thought process so far: Are we supposed to use the ratio of the densities to find this answer? like ##\frac{8g/cm^3}{2.7g/cm^3}##? and then use that...
  19. Ranku

    I Mass distribution in a celestial system

    If two sets of objects, of similar size but different mass, were to be part of a rotating celestial system, how differently would they be distributed? Would the distribution of the lower-mass objects be more spread out, while the higher-mass objects would be concentrated toward the centre?
  20. L

    I Do objects gain mass while approaching light speed?

    I watched a fermilab video claiming objects don't actually gain mass as they approach light speed. Is that true? What keeps things of mass from reaching the speed of light or beyond? I assume matter doesn't accumulate higgs-bosons while in motion?
  21. M

    B Does a body behave as a point mass even at rest?

    Hi, A body with center of mass behaves as a point mass when a force is applied. So when ##F_{ext}=0## then does it also behave as a point mass with ##a_{com}=0##, at rest. If yes, How can we prove this? (And can somebody please answer my other question I posted a week ago...
  22. C

    I What is the Order of Integration in a Double Integral?

    Hello everyone! I've been reading Mr. McMullen's book and took some curiosity in an equation on the cover art, it is as follows:$$y_{cm} = \frac \rho m \int_{r=0}^R\int_{\theta=0}^\pi (r\sin \theta)rdrd\theta$$I'm trying to understand what it means, firstly the limits of integration for the...
  23. S

    I Explaining how the Higgs fields gives particles mass

    Physicists say the Higgs Field is like syrup and slows particles down from the speed of light. Wouldn’t it be easier and more correct to say there are no particles, just fields, and the strength of the coupling of the electron, photon, quark etc. fields with the Higgs field determines their...
  24. K

    B Does Mass Have Lasting Gravitational Effect Over Time?

    I've been thinking about gravity. If mass contracts spacetime, can the warping effects be measured in time as well as spatial distance? For example -- say you had some matter that suddenly disappeared (please ignore the "how"). Measured in a fixed position, would the gravitational effect drop...
  25. Ranku

    I Celestial Systems: Mass & Distribution

    If two sets of objects, of similar size but different mass, were to be part of a rotating celestial system, how differently would they be distributed? Would the lower-mass objects be more diffusedly distributed, while the higher-mass objects be more concentrated toward the centre?
  26. N

    I Solving for the trajectory of the center of mass

    I'm working on the physics engine component of a game engine I'm building, and I need some guidance with this particular situation. Consider a square with mass M that is free to translate in the xy plane and free to rotate about any axis perpendicular to the page (Fig. 1) If a linear impulse J...
  27. JandeWandelaar

    I Will a spherical mass be set in motion by a spherical shell rotating around it?

    In general relativity, rotation of mass gives rise to framedraging effects, just like linear motion does, because of the off-diagonal components in the mass-energy-momentum tensor. So around Bonnor beams there is framedragging, as well around a rotating mass. Now imagine a spherical rotating...
  28. T

    I What is a typical mass density for inter-galactic gas in a cluster?

    I assume we can work it out from X-ray emission detections, such as shown with the famous bullet cluster images.
  29. Anonymous324

    I Electron mass conversion during electron capture

    In electron capture, a proton turns into a neutron and a neutrino is emitted. Is (without counting the mass difference between neutron and proton and the mass of the neutrino) the mass of the electron converted into energy in the form of gamma radiation?
  30. Rezex124

    I Damped oscillator with changing mass

    Hello, So about two weeks ago in class we looked at RLC circuits in our E&M course, and short story short... we compared the exchange of energy between the Capacitor and the Inductor (both ideal) to simple harmonic motion. Once the capacitor and inductor are not ideal anymore, we said it's...
  31. V

    Angular momentum of a disk about an axis parallel to center of mass axis

    I am using the following formula to solve this problem. $$ L_a= L_c + \text { (angular momentum of a particle at C of mass M)}$$ Because the point C is at rest relative to point A, so the second term in RHS of above equation is zero. Hence, the angular momentum about A is same as angular...
  32. alan123hk

    B The relationship between mass, light and energy

    I found that I had an inaccurate understanding of their relationship earlier. After rethinking, I try to express their relationship in a simple and understandable way Nuclear reactions convert energy from form of mass to form of light, and both energy and momentum are conserved during the...
  33. Y

    Momentum and impulse problem: A mass collides with another mass on a spring

    i would like to get some help and to understand why my answer is incorrect , here is how i did the first and second part. about the first part i did it right but i don't understand what I am doing wrong in the second part i tried -k and i get -23.997 and i also try +k and i get 23.997 but they...
  34. AspiringPhysicist12

    Block of mass M attached to rope of mass m

    We have the string's mass constraint m(x) = m(x/L). The block is accelerated right by force T(x=0) = Ma, where a = F / m + M. But at the point where the force is applied (i.e. x = L), I believe we have m(L/L)a = ma = F - T(L). But this would imply T(L) = F - ma = F - m(F / m + M) = F(M / m + M)...
  35. A

    Measurement of actual CO2 mass emitted from a diesel engine

    I was wondering if there is a method to measure the actual total mass of carbon dioxide (CO2) emitted from a diesel engine used with a generator for power generation (https://www.cat.com/en_US/products/new/power-systems/electric-power/diesel-generator-sets/1000028914.html). Infrared CO2 sensors...
  36. W

    I Energy Density in E Field: Does it Contribute to Inertial Mass?

    Hi. I'm not sure where to put this question, it concerns particles, mass-energy equivalence and various things. Classical electromagnetism seems to be as sensible a place as any. There is energy stored in an E field. Energy density (at position r, time t) = \frac{1}{2}...
  37. Rae

    How to express ωₙ in terms of only mass (m) and stiffness (k)?

    Summary: How to express ωₙ in terms of only mass (m) and stiffness (k)? I tried doing it with F=kx but it is out of my ability to simplify it to only m and k. Here is my approach:
  38. J

    A Mass dropped onto rotating disk

    Picture a flat disk of radius r with a radial vane. The disk is rotating at angular velocity w. Assume the vane is straight, starts at the center and ends at the perimeter of the disk. A very small round mass ( of m grams) is dropped onto the disk very near the center. The vane contacts it and...
  39. Green dwarf

    I Exploring Energy in Astronomy: Kinetic, Potential & Mass?

    I am planning to teach a school astronomy group about energy. Most people seem to accept that there are two types: kinetic energy, resulting from movement; potential energy, resulting from position in a force field with a potential gradient (convertible to KE if the object is allowed to move...
  40. U

    Mass Tipping a Plank: Independent & Dependent Variables + Data

    Can someone tell me what the Independent and Dependent variable is? And what is the data I'm supposed to collect? Is it the distance when the coins tip or is it the mass of the coins? Please help!
  41. technotux

    Heavy mass vs light mass in circular motion

    i think that the light sphere will go up higher(will have bigger acceleration) because there has to be a balance between the mass and the acceleration as long as the force is the same, for example if you push a heavy object and with the same force pushed another light object the light object...
  42. wcivch

    B Ride Gravitational Waves to Increase Speed?

    This is my first post so I apologize if i am in error anywhere. I recently had a thought that I have had trouble confirming. Based on the following assumptions. 1.) As you accelerate an object near the speed of light it’s mass increases exponentially. 2.) Mass warps space time. 3.) Spacetime...
  43. A

    I Mass & Density: Unpacking Feynman's Idea

    What do you think of the idea that mass is a number? This apparently derives from something Feynman said about energy. Apart from saying "nobody knows what energy is", he does go on to explain in the same lecture, what he knows about work energy. Is it more important to know how something is...
  44. S

    The torque required to rotate 675 lbs mass?

    Hello everyone, I am trying to design a fixture that can clamp onto and turn an equipment 180 degrees for maintenance. I am trying to figure out what torque will be required at the hand wheel to turn it. The piece of equipment will be clamped at its center of gravity. However, its mass is not...
  45. S

    Angular frequency of a mass performing SHM

    When given a small displacement ##x##, the equation for m is: (i) N sin θ = m.a where N is the normal force acting on the ball and θ is angle of the ball with respect to vertical. (ii) N cos θ = m.g So: $$\tan \theta = \frac a g$$ $$\frac x R = \frac{\omega^{2} x}{g} \rightarrow \omega = \sqrt...
  46. DuckAmuck

    A Unifying Lagrangians in Electrodynamics: Fμν, Aμ Jμ, & Lorentz Force

    How would you unify the two Lagrangians you see in electrodynamics? Namely the field Lagrangian: Lem = -1/4 Fμν Fμν - Aμ Jμ and the particle Lagrangian: Lp = -m/γ - q Aμ vμ The latter here gives you the Lorentz force equation. fμ = q Fμν vν It seems the terms - q Aμ vμ and - Aμ Jμ account for...
  47. LCSphysicist

    Rocket ejecting mass in a direction perpendicular to its velocity

    That was my approach: $$P_f - P_i = [(m-dm)(v + dv) + dm(u+v+dv)] - [m(v)]$$ $$= mdv - dmv + dmu + dmv = mdv + dmu = 0$$ Since the variation of the rocket's velocity is perpendicular to itself, $$ dv = v d \theta => m v d \theta + dm u = 0$$ So we have $$\frac{dm}{m} = \frac{-v d \theta}{u}$$...
  48. Grez

    Automotive How to calculate max car mass and tow capacity from motor specs?

    Hi I am trying to do an artisanal EV car and I would like to know how do I choose the right motor. I already have one in mind but I don't know how to calculate the max mass that it can move. (see attached pdf) Gear Ratio : 2.39 Diff Ratio : 4.88 Wheel Diameter: 26in I would like to know the...
  49. Isopod

    A CDF measures W mass higher than predicted

    The team has found that the particle, known as a W boson, is more massive than the theories predicted. The result has been described as "shocking" by Prof David Tobak, who is the project co-spokesperson. The discovery could lead to the development of a new, more complete theory of how the...
  50. Galois_

    Thermodynamics - Latent Heat Problem (finding mass)

    Can someone walk me through this? Our teacher didn't bother to meet us synchronously ever since and I'm kinda stumped on solving this. The equation I used for this problem is: mi = [mw(cw)(ti-tf)]/[Lfi + (Tf - Ti)] mi = [190(1)(23-3)]/[79.6+(3+20)] = 37.04g mi = mass of ice mw = mass of...
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