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A virtual particle is a theoretical transient particle that exhibits some of the characteristics of an ordinary particle, while having its existence limited by the uncertainty principle, which allows the virtual particles to spontaneously emerge from vacuum at short time and space ranges. [1]
Static force fields are fields, such as a simple electric, magnetic or gravitational fields, that exist without excitations.The most common approximation method that physicists use for scattering calculations can be interpreted as static forces arising from the interactions between two bodies mediated by virtual particles, particles that exist for only a short time determined by the ...
In computer programming, a static variable is a variable that has been allocated "statically", meaning that its lifetime (or "extent") is the entire run of the program. This is in contrast to shorter-lived automatic variables, whose storage is stack allocated and deallocated on the call stack; and in contrast to dynamically allocated objects, whose storage is allocated and deallocated in heap ...
The four-momentum of the virtual particle is the difference between the four-momenta of the incoming and outgoing particles. Virtual particles corresponding to internal propagators in a Feynman diagram are in general allowed to be off shell, but the amplitude for the process will diminish depending on how far off shell they are. [ 4 ]
However, C does vary strongly with discrete variables such as numbers of particles, and so it must be applied before summing over particle numbers. As mentioned above, the classic example of this overcounting is for a fluid system containing various kinds of particles, where any two particles of the same kind are indistinguishable and exchangeable.
If it is possible to find from the constraints as many independent variables as there are degrees of freedom, these can be used as generalized coordinates. [5] The position vector r k of particle k is a function of all the n generalized coordinates (and, through them, of time), [ 6 ] [ 7 ] [ 8 ] [ 5 ] [ nb 1 ]
Constraint force C and virtual displacement δr for a particle of mass m confined to a curve. The resultant non-constraint force is N . The components of virtual displacement are related by a constraint equation.
The static equilibrium of a mechanical system rigid bodies is defined by the condition that the virtual work of the applied forces is zero for any virtual displacement of the system. This is known as the principle of virtual work. [5] This is equivalent to the requirement that the generalized forces for any virtual displacement are zero, that ...