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  2. A look back at Action Line, the Detroit Free Press' famous ...

    www.aol.com/look-back-action-line-detroit...

    Action Line first asked readers to call in on Jan. 12, 1966, and received so many calls, it interfered with telephone service in downtown Detroit. Michigan Bell was forced to shut Action Line down ...

  3. Geodesics in general relativity - Wikipedia

    en.wikipedia.org/wiki/Geodesics_in_general...

    In general relativity, a geodesic generalizes the notion of a "straight line" to curved spacetime. Importantly, the world line of a particle free from all external, non-gravitational forces is a particular type of geodesic. In other words, a freely moving or falling particle always moves along a geodesic.

  4. Relativistic Lagrangian mechanics - Wikipedia

    en.wikipedia.org/wiki/Relativistic_Lagrangian...

    Alternatively, since we wish to build a Lagrangian out of relativistically invariant quantities, take the action as proportional to the integral of the Lorentz invariant line element in spacetime, the length of the particle's world line between proper times τ 1 and τ 2, [nb 1]

  5. Einstein–Hilbert action - Wikipedia

    en.wikipedia.org/wiki/Einstein–Hilbert_action

    The Einstein–Hilbert action in general relativity is the action that yields the Einstein field equations through the stationary-action principle. With the (− + + +) metric signature , the gravitational part of the action is given as [ 1 ]

  6. Metric tensor (general relativity) - Wikipedia

    en.wikipedia.org/wiki/Metric_tensor_(general...

    In general relativity, the metric tensor (in this context often abbreviated to simply the metric) is the fundamental object of study.The metric captures all the geometric and causal structure of spacetime, being used to define notions such as time, distance, volume, curvature, angle, and separation of the future and the past.

  7. Motion lines - Wikipedia

    en.wikipedia.org/wiki/Motion_lines

    In comics and art more broadly, motion lines (also known as movement lines, action lines, speed lines, [1] or zip ribbons) are the abstract lines that appear behind a moving object or person, parallel to its direction of movement, to make it appear as if it is moving quickly.

  8. Action principles - Wikipedia

    en.wikipedia.org/wiki/Action_principles

    Action principles are "integral" approaches rather than the "differential" approach of Newtonian mechanics.[2]: 162 The core ideas are based on energy, paths, an energy function called the Lagrangian along paths, and selection of a path according to the "action", a continuous sum or integral of the Lagrangian along the path.

  9. World line - Wikipedia

    en.wikipedia.org/wiki/World_line

    A world line of an object (generally approximated as a point in space, e.g., a particle or observer) is the sequence of spacetime events corresponding to the history of the object. A world line is a special type of curve in spacetime. Below an equivalent definition will be explained: A world line is either a time-like or a null curve in spacetime.