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Since the motion of a particle under a central force always lies in a plane, the position of the particle can be described by polar coordinates (r, θ 1), the radius and angle of the particle relative to the center of force (Figure 1). Both of these coordinates, r(t) and θ 1 (t), change with time t as the particle moves.
The problem of two fixed centers conserves energy; in other words, the total energy is a constant of motion.The potential energy is given by =where represents the particle's position, and and are the distances between the particle and the centers of force; and are constants that measure the strength of the first and second forces, respectively.
In astrodynamics, an orbit equation defines the path of orbiting body around central body relative to , without specifying position as a function of time.Under standard assumptions, a body moving under the influence of a force, directed to a central body, with a magnitude inversely proportional to the square of the distance (such as gravity), has an orbit that is a conic section (i.e. circular ...
The equation of motion for the particle derived above = + + can be rewritten using the definition of the Schwarzschild radius r s as = [] + + (+) which is equivalent to a particle moving in a one-dimensional effective potential = + (+) The first two terms are well-known classical energies, the first being the attractive Newtonian gravitational ...
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.
Suppose a target body is moving in a circular orbit and a chaser body is moving in an elliptical orbit. Let ,, be the relative position of the chaser relative to the target with radially outward from the target body, is along the orbit track of the target body, and is along the orbital angular momentum vector of the target body (i.e., ,, form a right-handed triad).
For two frames at rest, γ = 1, and increases with relative velocity between the two inertial frames. As the relative velocity approaches the speed of light, γ → ∞. Time dilation (different times t and t' at the same position x in same inertial frame) ′ =
Position space (also real space or coordinate space) is the set of all position vectors r in Euclidean space, and has dimensions of length; a position vector defines a point in space. (If the position vector of a point particle varies with time, it will trace out a path, the trajectory of a particle.)