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. L

    How Do You Derive and Analyze the Matrix for 3 Coupled Oscillators?

    Hi, I am not sure if I have derived the matrix correctly, because of my results in task b I solved task 1 as follows, I assumed that all three particles move to the right $$m \dot{x_1}=-k(x_1 - x_2)$$ $$2m \dot{x_2}=-k(x_2-x_2)-3k(x_2-x_3)$$ $$3m \dot{x_3}=-3k(x_3-x_2)$$ Then I simply...
  2. T

    B Mass of Space (B but approaching I)

    Since space is expanding, and that expansion moves things, then those moved things must be moved by something. If moved by space itself, then space must be providing the energy. And if gravity is a function of space and time interacting, then what is the energy or mass of a volume of space...
  3. Muu9

    I Change in orbit when mass is doubled

    A satellite is orbiting a planet in a circular orbit. The planet's mass doubles instantly. What happens to the orbit of the satellite? I think it would move to an elliptical orbit with major axis equal to the old radius and a minor axis equal to either 1/2 or sqrt(2)/2 times the old radius. I'm...
  4. PeterDonis

    Insights Why There Are Maximum Mass Limits for Compact Objects

    Continue reading...
  5. M

    The direction of flux vectors in derivation of conservation of mass

    In the derivation of the conservation law of the conservation of mass, the flux on one side enters and the flux on the other side leaves the control volume. I presume this is due to the assumption that the volume is infinitesimally small and hence v(x,y,z,t) will not change directions...
  6. N

    Proving SHM for charged spring mass system in electric field

    For part (f) Solution is I don't understand why the bit highlighted in yellow is true. Would anybody be kind enough to help.
  7. TerranIV

    B Shouldn't quantum gravity be an interaction between mass and spacetime?

    Einstein showed (via general relativity) that spacetime is curved by mass, mass moves in relation to this curvature, and that gravitation arises as secondary effect. Why then are we looking for quantum gravity as some sort of mass<->mass interaction? Aren't the fundamental interactions better...
  8. A

    I Is the mass of a photon stationary in space?

    I was reading a recent physics article on the google home page that stated that the current theory of mass is that it is a photon moving at light speed but stationary in space. My analogy of this was like a photon moving in a circle but it is not moving. I wish I could sight the article but...
  9. G

    I Calculating Mass Inertia Product - Examples 1 & 2

    How is the mass inertia product calculated? I have two examples and each one uses something different. Example 1: Example 2: moments and product of inertia of the cylinder
  10. T

    Exploring the Relationship Between Buoyancy and Apparent Mass

    my solution: a) F(upward)=Fb +Fw =(1.3+1.5)X9.8 =27.44N total Mass = 2.8kg b) Volume increased = π(0.2/2)^2 x 1.5/100 =4.7x10-4 m^3 T+Fb =mg T=mg-Fb T=2.2x9.8 -1000 x 4.7x10-4 x 9.8 T=17.4N T is the apparent weight of the rock, so the mass of the rock in the water...
  11. PeterDonis

    A Landau's Maximum Mass Limit Derivation in Shapiro & Teukolsky (1983)

    In Section 3.4 of Shapiro & Teukolsky (1983), a simple derivation, due to Landau, of the maximum mass limit for white dwarfs and neutron stars is given. I will briefly describe it here and then pose my question. The basic method is to derive an expression for the total energy (excluding rest...
  12. N

    I 3D Printed Piston | Lower mass = Power

    This is a piston I had DMLS printed from AlSi10mg - the geometry is derived from generative design using some basic inputs and a starting shape. It's really just an experiment whether a consumer grade design and print can be bolted in and work for a time. After machining, it is predicted to...
  13. uSee2

    Experimental Design: Pulley and Mass Hangers

    ^ This is my personal drawing of the diagram, I couldn't take a picture of the actual one. The setup is a pulley wrapped with a cord and mass hangers attached to each end. My first thought when approaching this problem was to first determine the rotational inertia of the pulley, then use some...
  14. M

    I Effective mass from the Lagrangian

    Hello! I have the following Lagrangian: $$L = \frac{1}{2}mv^2+fv$$ where ##v = \dot{x}##, where x is my coordinate and f is a function of v only (no explicit dependence on t or x). What I get by solving the Euler-Lagrange equations is: $$\frac{d}{dt}(mv+f+\frac{\partial f}{\partial v} v) =...
  15. marcosdb

    I Time dilation from galactic gravitational mass

    I've been thinking about how rotational speeds don't fall off high distances from galactic centers, for which dark matter is generally an explanation for the increase in acceleration Speed = distance / time But time is relative What "time" is used in these calculations? Wouldn't time be...
  16. M

    I How hard of a Hit force does it take to make a mass jump?

    I am looking for a formula that I can use to find out how high a steel rod or ball will jump up. If I hit mass M with force F how high will it jump up. If there is a program that would be great. every thing will be in pounds So if ball or rod of 10 lbs is hit on the bottem with 14 lbs of force...
  17. Spector989

    Variable mass, uniform body, force -- pulling a massive rope

    So i got some equations but i think i am missing something, my main doubt is what is the relation between dx / dt and v(o) [ here] . Workings in attachment
  18. H

    Solving for 'a' with Torque, Force, and Mass Moment of Inertia

    What I did was plug in the outer radius time the force into the torque and then the mass moment of inertia is equal to m*ro^2 so then I plugged in the mass times the radius of gyration squared into I and solved for a but this is not right.
  19. alan123hk

    B Is A Universe w/o Mass Possible? Exploring Time & Matter

    Is it possible to have a universe with only space and time but no mass ? I ask this question because a friend told me that time is an illusion. In fact, time does not exist. Because of the existence of matter, time can be felt through the movement of matter. If matter does not exist, time does...
  20. cory21

    Why can't I treat the disk as a point mass?

    Since the question made no indication of the disk rotating about its center, I just straight up assumed that the disk did not rotate about its center, and instead treated it as a point mass. However, to my surprise my calculations did not bear me any fruit. Below is my first attempt at the...
  21. MatinSAR

    Work and Energy for a mass sliding down a curved ramp (why does the ramp move?)

    What force causes the surface to move to the left? Can I say that it's due to the force component of the weight along the vertical force of the surface?
  22. D

    A box with the mass m = 25 kg is sliding up a hill

    What I have already attempted is on my Ipad and I don't know how to upload it on here. With hope of help DJ
  23. zuzelle

    How does this system work? (Four pulleys and a rope lifting a mass)

    I used the regular way of solving problems with pulleys. I tried to find the tension forces, which must be the same in the rope, but I get it wrong
  24. C

    Conservation of Energy with Mass on Hemisphere

    I tried approaching this question like this: F_N - mgcos(theta) = -mR(theta_dot)^2 and theta_dot = v/R since R is constant F_N = m(gcos(theta) - (v - v_0)^2/R) (with v being final velocity and v_0 being the initial velocity from the impulse) and then using energy conservation: at t = 0: E =...
  25. paulimerci

    Determine the net torque acting about the center of mass

    Net torque = 2gx20xcos30 - 2gx35xcos20 - 2gx15xcos60 + 2gx30xcos80 = -357Nm Have I done it right?
  26. A

    Angular Velocity from KE, radius, and mass

    I tried using the equation w^2 = (4*K)/(mr^2) but I don't think this is right... I got my answer to be 3.2243 and that's not correct
  27. Arwing

    Is Mass Irrelevant in This Problem?

    I'm not sure where to start, I feel like I'm missing the mass but it is not listed.
  28. Barbequeman

    Did I Calculate the Salpeter Initial Mass Function Correctly?

    I calculated the following in the attached file, I hope I did it correctly...
  29. kasnay

    Hanging mass on a massless pulley

    I have a conceptual question about this problem. I can write the 3.5 kg block equation as Fnet(block 1)=(Force of tension)-(Force of friction)=m1a I can write the 2.8 kg block as Fnet(block 2)=(Force of tension)-(Force of gravity2)=m2a My question is this If I set the forces of...
  30. Feynstein100

    B Could there be macro objects out there that convert energy to mass?

    Stars are basically large objects that convert mass to energy as allowed by the mass-energy equivalence in special relativity. So I was thinking, following the same equivalence, shouldn't the reverse be possible too? I.e. a kind of reverse star that sucks in energy and converts it into mass? I...
  31. mathbrain9

    Velocity comparison -- Which thrown mass hits the ground first?

    On the test, I said they hit the ground simultaneously. However, that, in retrospect, doesn't seem to be the correct solution.
  32. MatinSAR

    Mass on a Spring semi-submerged in a liquid

    Hi , Can someone tell me wether my answer is corrrect or false ?
  33. S

    Derive angular frequency for mass spring system

    tried writing the x position as x = Acos(wt) (ignoring the phase) so that d2x / dt2 = -w2x Substituting that into the individual motion equations would get the required result for the individual masses, but I am not sure how to combine the equations to get the reduced mass
  34. S

    How to find minimum possible mass

    Unfortunately, this is not the right answer.
  35. M

    A 4kg mass sits on a frictionless table....

    I got 13N but is that right because apparently, it's wrong Here's my work: F = mg = 2(10) = 20N F = ma a = F/m = 20/4+2 = 20/6 = 10/3 = 3.3m/s^2 T = mg - ma T = (2kg)(10m/s^2) - (2kg)(3.3m/s^2) = 13.4 N I appreciate it! And if I'm wrong could you show how you got your answer? Thanks
  36. dom_quixote

    B Tangran, Inertial Mass and Gravitational Mass

    Imagine a tangran puzzle, in which an extra piece "y", identical to piece 'x', is maliciously added. No matter how hard the player tries, he will never be able to restore the game's original form, that is: a perfect square. This illustration has a clear purpose: If gravitational mass and...
  37. 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...
  38. 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...
  39. 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...
  40. 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...
  41. 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!
  42. 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...
  43. 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...
  44. 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...
  45. 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.
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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