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If a coordinate q i is not a Cartesian coordinate, the associated generalized momentum component p i does not necessarily have the dimensions of linear momentum. Even if q i is a Cartesian coordinate, p i will not be the same as the mechanical momentum if the potential depends on velocity. [6] Some sources represent the kinematic momentum by ...
The energy and momentum of an object measured in two inertial frames in energy–momentum space – the yellow frame measures E and p while the blue frame measures E ′ and p ′. The green arrow is the four-momentum P of an object with length proportional to its rest mass m 0 .
Internal forces between the particles that make up a body do not contribute to changing the momentum of the body as there is an equal and opposite force resulting in no net effect. [3] The linear momentum of a rigid body is the product of the mass of the body and the velocity of its center of mass v cm. [1] [4] [5]
In modern notation, the momentum of a body is the product of its mass and its velocity: =, where all three quantities can change over time. Newton's second law, in modern form, states that the time derivative of the momentum is the force: F = d p d t . {\displaystyle \mathbf {F} ={\frac {d\mathbf {p} }{dt}}\,.}
There are two main descriptions of motion: dynamics and kinematics.Dynamics is general, since the momenta, forces and energy of the particles are taken into account. In this instance, sometimes the term dynamics refers to the differential equations that the system satisfies (e.g., Newton's second law or Euler–Lagrange equations), and sometimes to the solutions to those equations.
Position x and momentum p wavefunctions corresponding to quantum particles. The colour opacity of the particles corresponds to the probability density of finding the particle with position x or momentum component p. Top: If wavelength λ is unknown, so are momentum p, wave-vector k and energy E (de Broglie relations).
This equation states that the kinetic energy (E k) is equal to the integral of the dot product of the momentum (p) of a body and the infinitesimal change of the velocity (v) of the body. It is assumed that the body starts with no kinetic energy when it is at rest (motionless).
This has the advantage that kinetic momentum can be measured experimentally whereas canonical momentum cannot. Notice that the Hamiltonian ( total energy ) can be viewed as the sum of the relativistic energy (kinetic+rest) , E = γ m c 2 {\displaystyle E=\gamma mc^{2}} , plus the potential energy , V = q φ {\displaystyle V=q\varphi