What is Center: Definition and 1000 Discussions

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. alexmahone

    Hole drilled through center of the earth

    Suppose that a small hole is drilled straight through the center of the earth, thus connecting two antipodal points on its surface. Let a a particle of mass m be dropped at time t = 0 into this hole with initial speed zero. Find the period of the simple harmonic motion exhibited by the particle...
  2. 1

    Does Changing Material Density Affect the Center of Mass in a Composite Object?

    My textbook is giving awfully complicated formulas for centers of mass for actual objects (if they are a system of massive points, that's simpler for me.) Intuitively though, it just seems like it would be a weighted average?? So, If I have a solid metal cube, divided into two halfs...
  3. 1

    Integral Formulas for Center of Mass of Uniform Density

    Homework Statement I'm being given problems regarding the center of mass of a uniformly dense object, and I am told by the textbook to use: \frac{1}{V}\int x dV I have no idea what to do with that. I'm pretty sure I won't be learning anything about multiple variable integrals for two...
  4. 1

    Center of Mass Diagram Don't quite understand

    Homework Statement http://imageshack.us/photo/my-images/24/wtfdiagram.png/ Homework Equations The Attempt at a Solution I really haven't the slightest clue how to read this diagram. I see nothing resembling a U.
  5. D

    Center of mass question (man on a boat)

    Homework Statement A man with mass m1 = 60 kg stands at the left end of a uniform boat with mass m2 = 169 kg and a length L = 2.7 m. Positive x is pointing to the right. Assume there is no friction or drag between the boat and water. After the man walks to the right edge of the boat, what is...
  6. J

    How is center of mass in a complex systems?

    Now i am suddenly confused with the concept of the center of mass. As we know , nucleus are a system of many-body,composed of nucleons. And their interactions are very complex between nucleons. I want to know, If we can observe a nuclei such as Ne20, how is the motivation of its center of mass?
  7. M

    Finding circle center from two points and an arc length

    I'm trying to find the equation for a circle given two points in x, y and the starting angle, arc length, and two points along the circle. I need to find the equation because I need to translate a sprite along the curved path from one point to another. The situation ends up looking like this:A...
  8. A

    How do I determine the center of mass for a rod with varying linear density?

    Homework Statement A rod of length 36.00 cm has linear density (mass per length) given by λ = 50.0 + 21.5x where x is the distance from one end, and λ is measured in grams/meter. A. Find Total Mass B. Find center of mass from x=0 Homework Equations 1/M(integral)xdm , where M...
  9. C

    If center of galaxy is supermassive blackhole

    than why center is the brightest part of galaxy? shouldn't black hole suck all the light in? and if so, the more close to center of galaxy, the more time flow slower right? ...... English is not my native language, forgive me If I'm wrong in spelling or gamma
  10. T

    How to calculate center of gravity? emergency

    Sorry if this is posted in the wrong section I'm trying to find out what would be a good pick point on a steel point instead of just winging it. There are two sections to the steel pole, both combined together to create a total of 78 feet. The first section is 40' and weighs 3,438.004...
  11. J

    Electric field of semicircle rod at center

    [PLAIN]http://www.link-systems.com/sdkhtml/SDK/print/pr9849.gif
  12. J

    Electric field of a continuously charged semicircle rod at center

    Homework Statement A uniformly charged insulating rod of length 14.0 cm is bent into the shape of a semicircle. The rod has a total charge of -7.50\muC. Find (a) the magnitude and (b) the direction of the electric field at O, the center of the semicircle. Homework Equations...
  13. S

    Center of Mass Homework: Equations & Solution

    Homework Statement Homework Equations Please see attachment to #3. The Attempt at a Solution Apparently, the answer is Y= 4R/(3*pi). Why?
  14. M

    How Does Adding Ballast Affect the Center of Gravity in a Barge?

    Homework Statement <a href="http://www.flickr.com/photos/56362284@N04/6149231787/" title="untitled by redmond0991, on Flickr"><img src="http://farm7.static.flickr.com/6065/6149231787_e6230d69ab.jpg" width="407" height="229" alt="untitled"></a>...
  15. C

    Find the position of the center of mass of the binary star system

    Homework Statement A binary star system consists of a star P and a star Q, of mass 4.0 x 10^10 kg and 2.0 x 10^10 kg respectively, separated 6.3 x 10^9 m apart. Star P and Star Q move in circular orbits with their centers at the center of mass which remains at rest. Find the position of...
  16. S

    How to determine the center of mass of a runner?

    I have been reading a number of papers on the biomechanics of running and they all talk about the center of mass (COM), but I haven't found any description of how to determine the center of mass. I understand, for instance, that the center of mass moves forward with more forward lean. The...
  17. B

    Find the coordinates of a point on a circle without knowing the center point.

    Given 2 points on a circle, call them A and B. I know the cartesian coordinates of A. I also know the radius of the circle, the slope of the tangent line at A, and the length and direction of the arc between A and B. I don't know the coordiates of the center of the circle. How do I find...
  18. C

    Does the Center of Mass Affect Gravity?

    I was thinking that objects like a sphere have a center of mass in the middle of the sphere and also if you were in the middle of the sphere you would feel no gravitational pull in any direction. So then I was wondering if all objects had a zero gravitational pull at their center of mass. But...
  19. L

    Center of Mass and Inertia Tensor Experimentation

    Hello All, I am trying to create an experiment to determine the center of mass and inertia tensor of an aribtrary object. This object is small (softball size), and non symmetrical on all axis. I have some thoughts concerning gyroscopes and accelorameters, but am curious to see what thoughts...
  20. C

    Center mass of triangle in 3-D space

    Homework Statement So I have a triangle with points: A (4,2,0), B (3,3,0), and C (1,1,3). We are to find the point at which the three medians intersect in i,j,k format. I've found the midpoints of each side but I don't know where to go from there.
  21. I

    Center of mass of a hemisphere

    As part of a problem I need to find the center of mass of a hollow hemisphere. I did it in the following way. I considered the lower hemisphere ( around negative z axis ) First by definition, the position vector of the center of mass is obtained as \vec{R}=...
  22. J

    The electric field at the center of a square

    http://helios.augustana.edu/~dr/203/probs/Set%201.pdf Scroll down to #11 for a picture. So I kind of understand the math. I am a little confuse though. So why is a divided by sqrt(2)? If this is a vector, then the center is really (a(sqrt(2)))/2 and the x component would be divided by...
  23. B

    How Does the Center of Mass Move in a Block and Wedge System?

    Homework Statement A large wedge rests on a horizontal frictionless surface. A block starts from rest and slides down the inclined surface of the wedge, which is rough. During the motion of the block, the center of mass of the block and wedge. a. does not move. b. moves horizontally with...
  24. F

    Electric Field at the center of a square

    Homework Statement Calculate the electric field (magnitude & direction) at the center of a square 52.5 cm on a side if one corner is occupied by a = -38.6 µC charge and the other three are occupied by -27.8 µC charges. Homework Equations Enet= E1center + E2center + E3center + E4center...
  25. K

    Designing a power supply with a center tapped-transformer and a zener diode.

    Homework Statement Design a full-wave regulated power supply using a 5:1 center-tapped transformer and a 7.5 V, 1 W Zener diode. The power supply must provide a constant 7.5 V to a load varying from 120 to 450 . The input voltage is 120 V(rms), 60HZ.Homework Equations The Attempt at a Solution...
  26. M

    Center of mass to find support reactions at pins for a homogeneous flat plate

    Homework Statement The mass of the homogeneous flat plate is 50 kg. Determine the reactions at the supports A and B. I've attached the diagram. The Attempt at a Solution I know I will need to find the center of mass. I don't remember exactly how to do it, but I found the centroid...
  27. Dotini

    Infinity at the Center of the Galaxy

    "Infinity" at the Center of the Galaxy http://www.sciencedaily.com/releases/2011/07/110719151234.htm http://www.wired.com/wiredscience/2011/07/milky-way-ribbon/ New observations from the Herschel Space Observatory show a bizarre, twisted ring of dense gas at the center of our Milky Way...
  28. T

    Calculating the direction of the center of the universe?

    Calculating the direction of the "center" of the universe? I've had a theory lingering in my consciousness for a long time. I've wondered about the relevance between the speed of light, red-shift in stars and galaxies and relativity. Although c is a constant, I have read somewhere that...
  29. H

    Initiate Research and development center

    Am studying electrical engineering, i was wondering about how to initiate research and development in engineering field, and how to select and find the ideas that will be studied and solved. Suppose a study is done, for whom this new technology will be sold and who will save your rights...
  30. Simfish

    Does NASA Ames Research Center have a graduate school?

    Chris McKay told me that they do take grad students, but I can't find any more information on the Internet (the Ames page points to a dead link for the "Graduate Student Researchers Program") - see http://hr.arc.nasa.gov/student/gradfaculty.html
  31. R

    How Is the Center of Mass Calculated in a Balancing Torque Problem?

    Homework Statement A 1.0 kg rock is suspended by a massless string from one end of a 1.0 m long measuring stick. What is the mass of the measuring stick if it is balanced by a support at the 0.25 m mark? Homework Equations Torque=(distance perpendicular to force from the center of...
  32. D

    Finding the center of mass of a rod

    This is a pretty tough question for me. I am trying to learn, so please no rude people or trolls please. Here is the problem I was given. A 50 dyne steel rod is fixed at a point 20cm. from the right end. The clamp at this point provides a force of 200 dynes upward. The rod is in equilibrium...
  33. S

    Beam with simple support at center

    uniformly distributed load on a beam. it has a single simple support at the center of gravity. Beam length L and load distribution w (pounds/inch) How do I find the shear and moment diagrams?
  34. N

    Specify the position of the center of mass

    Homework Statement Two identical uniform rectangular flat planks with sides a and b are glued together to form a T-shaped object. Specify the position of the center of mass. State any theorems you use in order to arrive at your conclusion. See the attempted solution for a diagram. :) The...
  35. N

    Center of gravity and Newton's 3 Law of Motion.

    I have a project to do and I have to make a demonstration about a physics phenomenon. I'n planning on doing a demonstration that explains one or all of Newton's Laws of Motion. I've chosen to do it on the center of gravity, but I want to know if it's related to Newton's 3 Laws of Motion or is it...
  36. C

    Why can't there be a center of relativistic mass?

    As the title. More specifically, with respect to the center of momentum frames massless particles don't have, why not if they still do have relativistic mass? (Bracing for an easy answer to a stupid question...) :redface:
  37. A

    Finding the Center of Mass of a Wing

    Homework Statement so we have this engineering assignment (high school final year) where we have to design an airplane wing and one of the tasks is to (graphically, not all of us can even differentiate let alone mathematically derive it) identify the center of mass of the wing... now, i know...
  38. Y

    Are we at the center of the universe and whats at the edge?

    I am wondering about the size of the universe. I have read that we can only "see" 13.7 billion light years away in all directions and that we are in the center. To my mind this presents a problem. The problem is what are the odds that we are in the center of the universe? Then again even...
  39. fluidistic

    Boas Mathematical physics book, definition of center of mass

    In Boas' book I can read that the definition of center of mass of a body has coordinates x_{CM}= \int x_{CM}dM= \int x dM. Shouldn't it be this same integral but divided by M?! Also, I didn't find the definition of center of mass for particles or any non continuous bodies. I'd be grateful if...
  40. zimo

    B field at the center of a large charges sheet

    Homework Statement In a plastic film factory, a wide belt of thin plastic material is traveling between two successive rollers with the speed v. In the manufacturing process, the film has accumulated a uniform surface electric charge density σ. What is B near the surface of the belt in...
  41. P

    Finding the center by area of a range of a sine wave

    hey. I used to be quite talented at math, but I've let my talent deteriorate in the ~10 years since my last calculus class. I have a problem which I'm sure I would have devoured easily back in my school days, but am having trouble with now. I am considering two points on a normal (0 to...
  42. K

    How Do You Calculate the Distance Between Two Stars in a Binary System?

    Homework Statement 2 stars are separated by a distancce r, one star has mass 2/3M the other has mass 2M (M is a solar mass). The period of revolution is 5 years, calculate r. Homework Equations Fg=(GM1M2)/r^2 The Attempt at a Solution Ok so I know that the binary star...
  43. B

    Strange: Earth's center of gravity

    Hi there, so I'm a bit confused...I'm 14 years old and I'm living in Croatia.I heard for Hallow Earth theory one year ago so I wanted to research it, but I had no material i needed until today...data(material9 i needed is what is radius of Earth on poles and Equator and what g is there...
  44. H

    What is a roll center? (steady state cornering in a vehicle)

    I'm studying the chapter 'Steady State Cornering', from the book 'Fundamentals of Vehicle Dynamics' (by Gillespie). The concept of a 'roll center' seems to be very important here, especially after the 'roll axis' is defined (line joining the front and rear roll centers). But I don't...
  45. T

    Can we go through the center of the Earth

    Hello, i need help on this question, i have been thinking about it assume there is a hole through the center of the Earth , and oxygen is exist so we can breath , if we drop the ball into the hold, is it possible for ball go through the center of the Earth to other side of the hole ? so what i...
  46. Femme_physics

    Dividing over zero while calculating center of gravity - Getting error

    Homework Statement Calculate the center of gravity of this object: http://img638.imageshack.us/img638/8412/inddddd.jpg The Attempt at a Solution The bottom line turns out zero, so I get something over zero therefor error! http://img101.imageshack.us/img101/6995/theretherere.jpg
  47. Islam Hassan

    Big Bang With No Center Fallacy?

    Either the Big Bang began in a small, restricted area/volume/domain/node/etc or the universe sprang into existence "everywhere all at once" -whatever that means- as I once read somewhere (to explain why the universe has no center). So which is it? And if it sprang into existence in a homogenous...
  48. C

    Center of mass of tetrahedron with uniform density

    Hi, I have 4 non-planar points P1 = ( x1 , y1 , z1 ) P2 = ( x2 , y2 , z2 ) P3 = ( x3 , y3 , z3 ) P4 = ( x4 , y4 , z4 ) what is the coordinate of center of mass of the object ( tetrahedron ) whose vertices are P1 P2 P3 and P4? ( uniform density ) Thanks
  49. Femme_physics

    Center of gravity - conflicting result

    From some reason Yc's result is different than mine. But, the solution manual and me are using the same X axis to calculate Yc (we're using a different Y axis to calculate Xc, though). Can someone explain to me what's wrong here?The question: Calculate the center of mass of the material line...
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