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  2. Dynamical friction - Wikipedia

    en.wikipedia.org/wiki/Dynamical_friction

    The effect of dynamical friction explains why the brightest (more massive) galaxy tends to be found near the center of a galaxy cluster. The effect of the two body collisions slows down the galaxy, and the drag effect is greater the larger the galaxy mass. When the galaxy loses kinetic energy, it moves towards the center of the cluster.

  3. Spacecraft flight dynamics - Wikipedia

    en.wikipedia.org/wiki/Spacecraft_flight_dynamics

    A space vehicle's flight is determined by application of Newton's second law of motion: =, where F is the vector sum of all forces exerted on the vehicle, m is its current mass, and a is the acceleration vector, the instantaneous rate of change of velocity (v), which in turn is the instantaneous rate of change of displacement.

  4. Friction - Wikipedia

    en.wikipedia.org/wiki/Friction

    Fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. [7] [8] Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces. [9] [10] [11] Skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body.

  5. Problem of time - Wikipedia

    en.wikipedia.org/wiki/Problem_of_time

    The field equations of general relativity are not parameterized by time but formulated in terms of spacetime. Many of the issues related to the problem of time exist within general relativity. At the cosmic scale, general relativity shows a closed universe with no external time. These two very different roles of time are incompatible. [4]

  6. Two-body problem in general relativity - Wikipedia

    en.wikipedia.org/wiki/Two-body_problem_in...

    In the Schwarzschild solution, it is assumed that the larger mass M is stationary and it alone determines the gravitational field (i.e., the geometry of space-time) and, hence, the lesser mass m follows a geodesic path through that fixed space-time. This is a reasonable approximation for photons and the orbit of Mercury, which is roughly 6 ...

  7. n-body problem - Wikipedia

    en.wikipedia.org/wiki/N-body_problem

    In physics, the n-body problem is the problem of predicting the individual motions of a group of celestial objects interacting with each other gravitationally. [1] Solving this problem has been motivated by the desire to understand the motions of the Sun, Moon, planets, and visible stars.

  8. Force field (physics) - Wikipedia

    en.wikipedia.org/wiki/Force_field_(physics)

    In physics, a force field is a vector field corresponding with a non-contact force acting on a particle at various positions in space. Specifically, a force field is a vector field F {\displaystyle \mathbf {F} } , where F ( r ) {\displaystyle \mathbf {F} (\mathbf {r} )} is the force that a particle would feel if it were at the position r ...

  9. Vacuum energy - Wikipedia

    en.wikipedia.org/wiki/Vacuum_energy

    A field in physics may be envisioned as if space were filled with interconnected vibrating balls and springs, and the strength of the field is like the displacement of a ball from its rest position. The theory requires "vibrations" in, or more accurately changes in the strength of, such a field to propagate as per the appropriate wave equation ...