Center of mass rigid body, the gravity forces will not cause the body to rotate, which means the weight of the body can be considered to be concentrated at the center of mass. The linear and angular momentum of a collection of particles can be simplified by measuring the position and velocity of the particles relative to the center of mass. Let the system of particles "P", "i"=1...,"n" of masses "m" be located at the coordinates r with velocities v. Select a reference point R and compute the relative position and velocity vectors, The total linear and angular momentum vectors relative to the
Pulse wave velocity in the investigation of hypertension. The theory of the velocity of the transmission of the pulse through the circulation dates back to 1808 with the work of Thomas Young. The relationship between pulse wave velocity (PWV) and arterial wall stiffness can be derived from Newton's second law of motion (formula_1) applied to a small fluid element, where the force on the element equals the product of density (the mass per unit volume; formula_2) and the acceleration. The approach for calculating PWV is similar to the calculation of the speed of sound, formula_3, in a compressible fluid (e.g. air): formula_4, where