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In geometry, a straight line, usually abbreviated line, is an infinitely long object with no width, depth, or curvature, an idealization of such physical objects as a straightedge, a taut string, or a ray of light. Lines are spaces of dimension one, which may be embedded in spaces of dimension two, three, or higher.
The line of action is shown as the vertical dotted line. It extends in both directions relative to the force vector, but is most useful where it defines the moment arm. In physics , the line of action (also called line of application ) of a force ( F → ) is a geometric representation of how the force is applied.
For example, in Book I of Euclid's Elements, a line is defined as a "breadthless length" (Def. 2), while a straight line is defined as "a line that lies evenly with the points on itself" (Def. 4). Euclid's idea of a line is perhaps clarified by the statement "The extremities of a line are points," (Def. 3). [3]
The upper curve is the line of liquidus, and the lower curve is the line of solidus. In chemistry , materials science , and physics , the liquidus temperature specifies the temperature above which a material is completely liquid, [ 2 ] and the maximum temperature at which crystals can co-exist with the melt in thermodynamic equilibrium .
A baseline in science (including medicine) is the initial conditions found by observation and measurement at the beginning of a survey or clinical trial or which is used for comparison with later data collected during or after the survey or trial to identify and measure changes, often with the intention of assessing the effects of a treatment or procedure.
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.
Line a is a great circle, the equivalent of a straight line in spherical geometry. Line c is equidistant to line a but is not a great circle. It is a parallel of latitude. Line b is another geodesic which intersects a in two antipodal points. They share two common perpendiculars (one shown in blue).
3. Between two groups, may mean that the second one is a proper subgroup of the first one. ≤ 1. Means "less than or equal to". That is, whatever A and B are, A ≤ B is equivalent to A < B or A = B. 2. Between two groups, may mean that the first one is a subgroup of the second one. ≥ 1. Means "greater than or equal to".