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The experimental determination of a body's center of mass makes use of gravity forces on the body and is based on the fact that the center of mass is the same as the center of gravity in the parallel gravity field near the earth's surface. The center of mass of a body with an axis of symmetry and constant density must lie on this axis.
A special case of the center-of-momentum frame is the center-of-mass frame: an inertial frame in which the center of mass (which is a single point) remains at the origin. In all center-of-momentum frames, the center of mass is at rest , but it is not necessarily at the origin of the coordinate system.
Total energy is the sum of rest energy = and relativistic kinetic energy: = = + Invariant mass is mass measured in a center-of-momentum frame. For bodies or systems with zero momentum, it simplifies to the mass–energy equation E 0 = m 0 c 2 {\displaystyle E_{0}=m_{0}c^{2}} , where total energy in this case is equal to rest energy.
The total center of mass of the forks, cork, and toothpick is on top of the pen's tip. Significant aspects of the motion of an extended body can be understood by imagining the mass of that body concentrated to a single point, known as the center of mass. The location of a body's center of mass depends upon how that body's material is distributed.
The following is a list of centroids of various two-dimensional and three-dimensional objects. The centroid of an object in -dimensional space is the intersection of all hyperplanes that divide into two parts of equal moment about the hyperplane.
F = total force acting on the center of mass m = mass of the body I 3 = the 3×3 identity matrix a cm = acceleration of the center of mass v cm = velocity of the center of mass τ = total torque acting about the center of mass I cm = moment of inertia about the center of mass ω = angular velocity of the body α = angular acceleration of the body
The total mass is the zeroth moment of mass. The center of mass is the 1st moment of mass normalized by total mass: R = 1 M ∑ i r i m i {\textstyle \mathbf {R} ={\frac {1}{M}}\sum _{i}\mathbf {r} _{i}m_{i}} for a collection of point masses, or 1 M ∫ r ρ ( r ) d 3 r {\textstyle {\frac {1}{M}}\int \mathbf {r} \rho (\mathbf {r} )\,d^{3}r} for ...
where μ is the reduced mass and r is the relative position r 2 − r 1 (with these written taking the center of mass as the origin, and thus both parallel to r) the rate of change of the angular momentum L equals the net torque N = = ˙ ˙ + ¨ , and using the property of the vector cross product that v × w = 0 for any vectors v and w ...