Center Definition and 1000 Threads

In physics, the center of mass of a distribution of mass in space (sometimes referred to as the balance point) is the unique point where the weighted relative position of the distributed mass sums to zero. This is the point to which a force may be applied to cause a linear acceleration without an angular acceleration. Calculations in mechanics are often simplified when formulated with respect to the center of mass. It is a hypothetical point where the entire mass of an object may be assumed to be concentrated to visualise its motion. In other words, the center of mass is the particle equivalent of a given object for application of Newton's laws of motion.
In the case of a single rigid body, the center of mass is fixed in relation to the body, and if the body has uniform density, it will be located at the centroid. The center of mass may be located outside the physical body, as is sometimes the case for hollow or open-shaped objects, such as a horseshoe. In the case of a distribution of separate bodies, such as the planets of the Solar System, the center of mass may not correspond to the position of any individual member of the system.
The center of mass is a useful reference point for calculations in mechanics that involve masses distributed in space, such as the linear and angular momentum of planetary bodies and rigid body dynamics. In orbital mechanics, the equations of motion of planets are formulated as point masses located at the centers of mass. The center of mass frame is an inertial frame in which the center of mass of a system is at rest with respect to the origin of the coordinate system.

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  1. ari-anne

    Finding the center of gravity with torque

    I don't know how to find the center of gravity much less in this problem, so I just created a diagram of the pole with all the forces.
  2. J

    Understanding Output Voltages for a Center Tapped Transformer

    While trying to understand the working of a full wave rectifier I was unable to precisely understand the working of the central tap transformer. Edit 1 : The voltages are out of phase by 180 degrees as voltage is alternating(?) So the only thing I don't understand is how the distribution of...
  3. 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...
  4. Amik

    Velocity of the center of mass of the system

    I believe they are the same?I think i am wrong.
  5. 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...
  6. S

    Electrical Load center terminal screws - where to buy?

    Where can a person buy the small screws that hold the wires into terminals in a SquareD brand load center (breaker box) ? Places sell the screws that hold the panel cover on a a breaker box. They also sell the "lugs" that hold very large wires. However, what I'd like is a package of the...
  7. Indula

    How to calculate the inductance of a center tapped solenoid ?

    I'm trying to drive a transformer using a ZVS power supply. The primary coil that we use here has to be wound center tapped. The output frequency depends on the inductance of the primary winding and capacitance used in the circuit. The circuit of a ZVS power supply is as follows, The...
  8. LordWhiplash

    I Why is the lowest energy level close to the center?

    While studying photon emission, I noticed that I never really understood why the higher energy level is farther from the center of the atom. To me it seems counterintuitive, because usually the forces of attraction are greater at shorter distances, which would imply a higher energy consumption...
  9. 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...
  10. lLehner95

    Find the photon energy in the center of mass frame and vice versa

    I tried to use the Lorentz transformation: ##E^{*}_{\gamma }=\gamma _{cm}E_{\gamma }-\beta _{cm}\gamma _{cm}p_{\gamma }## We have a photon, so it becomes: ##E^{*}_{\gamma }=\gamma _{cm}E_{\gamma }(\beta _{cm}-1)## Unfortunately, the solutions say that the correct way is to use the inverse...
  11. B

    I Calculating Bin Center for Rate vs Energy Plot

    Hello! I want to plot a rate vs energy plot, but I am not sure how assign the bin center. Assume I have 2 data points in the bin (so 2 energy values), ##E_1## and ##E_2## and the first one has 100 counts measured over 10 seconds (so a rate of 10 counts/s) while the second one has 2000 counts...
  12. Nimarjeet Bajwa

    How can we find the center of mass of a solid cone?

    is this method even possible? anyways here is my attempt Step1) y= 2H/3 ( H is the height of the cone) step 2) we take the density (ρ)= 3M/π R2 H. The problem i am facing is to Find "dm"
  13. Jelsborg

    Electric field of a spherical conductor with a dipole in the center

    In a recent test we were asked to calculate the electric field outside a concentric spherical metal shell, in which a point dipole of magnitude p was placed in the center. Given values are the outer radius of the shell, R, The thickness of the shell, ##\Delta R## and the magnitude of the dipole...
  14. Euge

    MHB What Is the Center of the Ring of All \( n \times n \) Complex Matrices?

    Here is this week's POTW: ----- Compute the center of the ring $M_n(\Bbb C)$ of all $n\times n$ complex matrices. ----- Remember to read the https://mathhelpboards.com/showthread.php?772-Problem-of-the-Week-%28POTW%29-Procedure-and-Guidelines to find out how to...
  15. JD_PM

    I Two rings rotating about a common center

    Problem statement: Two rings rotate with equal and opposite angular (relativistic) velocity about a common center. Matt rides on one ring and Eve on the other and there's a moment they meet and their clocks agree. At the moment they pass by one another, each asserts that is the other's clock...
  16. jisbon

    Help Me Solve My Diagram Problem: Calculating Center of Mass

    Not sure what I went wrong here, anyone can help me out on this? Thanks. EDIT: Reformatted my request. Diagram: So as far as I know to calculate the center of mass for x, I have to use the following equation: COM(x): ##\frac{1}{M}\int x dm## And I also figured that to find center of mass, I...
  17. Like Tony Stark

    ##\vec v## and ##\vec a## expressions - motion on an off center circle

    Well, I tried decomposing velocity into its components on the radial and angular axis. But I have problems with the angles because in some parts of the trajectory the velocity is on the angular coordinate, but in other parts it isn't. I mean, I can't say ##V=V e_\theta## because it's not always...
  18. Seth Greenberg

    What is the angular velocity in the center of a rotating disc?

    I have a disc. The center of the disc is its center of mass and the motion of the disc is purely rotational (no translation). What is the angular velocity in the center of the rotating disc?
  19. paulmdrdo

    Engineering Finding the center frequency and bandwidth of a Pass-band filter

    I tried solving this problem and got it correctly until the part A of the question. My solution is the same as the one given in the solutions manual until the part I put in the red box. I don't understand what is the logic behind the calculation of the bandwidth and center frequency there...
  20. Prabs3257

    Velocity of the center of mass in constrained motion

    I tried getting the velocity of a which by using constraint came out to be 3 and by using the eqn for vcom i got the ans as 3.5 i just want to confirm is this the correct answer
  21. jordy1380

    Intro Physics Principles of Technology by the Center for Occupational Research and Development

    I am beginning to teach physics this fall and the previous teacher used Principles of Technology (PT) for a remedial physics course. I have all of the textbooks for this class along with the teacher materials but there is no planning information in regards to pacing, how to use the text in...
  22. 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...
  23. F

    Reflection and Rotation Centers in D_n: Finding C(F) and C(R) for Even and Odd n

    Let ##F_0## be a reflection in ##D_n## s.t. ##F \neq F_0##. Observe, ##F_0F = FF_0## is equivalent to ##F_0FF_0F = (F_0F)^2 = R_0##. Since a reflection followed by a reflection is a rotation, and the only rotation of order 2 is ##R_{180}##, we have ##F_0F = R_{180}##. Thus, ##F_0F = FF_0## is...
  24. 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...
  25. 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...
  26. Benjamin_harsh

    Is it possible to use the center of gravity to balance a bird toy?

    Here is the picture where person balancing a toy bird with using center of mass. I am bored with center of mass. I want to try same experiment with center of gravity. Is it possible to use center of gravity to balance bird toy ?
  27. S

    Fixed-End Beam with Center Static Load

    The bracket shown in figure 1 is applied to both ends of a beam (figure 2) which experiences a single static load at its center. The bottom of both brackets are fixed by some method, so it can't deflect. According to Solidworks, the bracket survives with flying colors, but it bothers me that I...
  28. arcTomato

    How can we determine the distance to the Galactic center?

    Problem Statement: We can use "spectroscopic line shift of S2" and "its proper motion", but I don't have any idea what dose this sentences mean. please show me details! Relevant Equations: spectroscopic line shift
  29. 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...
  30. 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...
  31. 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...
  32. S

    Center surround detection explained?

    A while back I asked about human vision processing and if it is performed synchronously or asynchronously. One of the responses mentioned that the retina performs 'Center Surround Detection'. So I tried to google what this is but no relevant results came up. Is anyone able to explain what this...
  33. R

    What is the solution to the Center of Mass problem?

    I was able to find the y and z axis. To find the x-axis I was assuming they would be the same for both of the slab parts and since the center of mass is the middle of the cube it should be halfway between 14.0 cm, which is 7.0cm. I can't think of any other reason why it would not be.
  34. C

    MHB How can we prove that the center of a ring is a subring?

    Dear Everyone, I am stuck on a portion of the sub-ring criterion. The Problem states: "The center of a ring $R$ is $\{z\in R| zr=rz \ \forall r\in R\}$. Prove that the center of the ring is a subring that contains the identity as well as the center of a division ring is a field." I am doing...
  35. Lone Wolf

    Finding the center of mass of a homogeneous object

    The object is: My attempt at a solution: I divided the object into 3 different rectangles and found the coordinates for the center of mass of each one, considering the origin at point "O". Then I found the mass of each rectangle, assuming the object has an area density of σ. m1 = 15σ; m2= 6σ...
  36. RicardoMP

    How to determine particle energies in center of momentum frame?

    That said, my approach was to determine the energies and 3-momenta at the center of momentum reference frame for each particle, with a fixed s, and check it corresponds to each one of the above, but I'm having some trouble proving that, for example, E_A=\frac{s+m^2_A-m^2_B}{2\sqrt{s}}. I've...
  37. P

    I Center of Mass of a jetpack-Earth System

    It is known that the center of mass of an isolated system will assume the same location no matter what internal forces there are (as long as no net external force occurs). My first question is if there exist two bodies of masses m1 and m2 in some space that has no friction, gravity, or...
  38. D

    How to find the center of mass of a cube?

    Homework Statement Find the center of mass of a homogeneous solid cube with side ##L## analytically. Homework Equations None. The Attempt at a Solution I don't understand how to find the center of mass on three dimensions. I know that since it is homogeneous, if I center the cube on the...
  39. D

    Find the center of mass of a plate

    Homework Statement Find the center of mass of the next plate if: A) Is homogeneous B) Its density per unit mass is ##\sigma=Axy##, where ##A## is a constant. Homework Equations ##X_{cm}=\frac{\int\sigma x dA}{\int\sigma dA}## ##Y_{cm}=\frac{\int\sigma y dA}{\int\sigma dA}## The Attempt at a...
  40. J

    Finding the POSITION of the center of mass

    Homework Statement Three spheres are placed around a coordinate grid: one of mass m at the bottom-left, one of mass 3m a distance of 3L above the first, and one of mass 2m a distance of 4L to the right of the first. 4 points between these three spheres are labeled: A near (1.3L, 1.5L), B...
  41. H

    Effect of the Location of the Center of Mass on the Falling Time....

    The set-up of the system is like the following: The thing is, a weight was attached to the meter stick and it was placed in different locations. Then the system composed of the meter-stick and the added weight was then released and the time it took for the meter stick to hit the floor was...
  42. E

    Where is my mistake? (Pure rolling and center of mass)

    Homework Statement A cylinder with a mass of M and radius R is attached to a spring with a constant of k. The attachment always stays the same as described in the picture. The cylinder is moved to the right and the released, and it rolls without slipping (pure rolling). What will be the...
  43. Zack K

    Potential at center of sphere of radius R and charge -Q

    Homework Statement What is the potential at the center of the sphere relative to infinity? The sphere is dielectric with uniform - charge on the surface of the sphere. Homework Equations ##k=\frac {1}{4\pi\epsilon_0}## ##V=\frac {KQ}{r}## The Attempt at a Solution If the distance r=0 it would...
  44. Athi Sankar

    Why does radial acceleration act toward the center?

    Acceleration of a rotating link has two components,Tangential (change in the direction) Radial (change in the magnitude). Why the direction of Radial acceleration is considered towards center (Centripetal)? what about centrifugal?
  45. K

    Problem when calculating the center of mass of a triangle

    Homework Statement if the black dot is assumed by (0,0).find the center of mass coordinate of this triangle [/B] i'm sorry but since the pic won't show ill attach the link here https://ibb.co/4Ptw5T7 <Moderator's note: picture added> Homework Equations centroid is 2/3 of median [/B] using...
  46. Hiero

    Torque about center of mass due to Coriolis force, is it 0?

    It’s essentially a question about cross product identities. I want to analyze a problem in a frame of reference which is rotating with angular velocity ##\vec \Omega## relative to an inertial frame. In this non-inertial frame, we have a rigid body rotating with constant angular velocity ##\vec...
  47. D

    Equilibrium : normal reaction of a rotational center?

    Homework Statement I'm trying to figure out the reaction at D,that's where the system can rotate. Problem: A force P of magnitude 90 N is applied to member ACDE, which is supported by a frictionless pin at D and by the cable ABE. Since the cable passes over a small pulley at B, the tension...
  48. E

    Angular momentum conservation and center of mass

    Homework Statement Two bodies with an equal mass of M are attached by a pole with no mass with a length of L. The system is placed on a horizontal table and at first it is at rest. At t=0 a bullet with a mass of m hits the pole, as described in the picture. The collision is completely elastic...
  49. F

    Body rotating about its center of mass

    Hello, As many know, when an external force acts on a rigid body and the force's line of action does not pass through the body's center of mass ##c.m.##, the force will cause the body to both translate and rotate exactly about the ##c.m.##. Otherwise, the body will solely translate without...
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