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  2. Necessity and sufficiency - Wikipedia

    en.wikipedia.org/wiki/Necessity_and_sufficiency

    The assertion that Q is necessary for P is colloquially equivalent to "P cannot be true unless Q is true" or "if Q is false, then P is false". [9] [1] By contraposition, this is the same thing as "whenever P is true, so is Q". The logical relation between P and Q is expressed as "if P, then Q" and denoted "P ⇒ Q" (P implies Q).

  3. Van der Waals equation - Wikipedia

    en.wikipedia.org/wiki/Van_der_Waals_equation

    The solid green lines represent stable states, and terminate at dots that represent the saturated liquid and vapor states that comprise the phase change. The dashed green lines represent metastable states ( superheated liquid and subcooled vapor) that are created in the process of phase transition, have a short lifetime, and then devolve into ...

  4. Phase rule - Wikipedia

    en.wikipedia.org/wiki/Phase_rule

    In thermodynamics, the phase rule is a general principle governing multi-component, multi-phase systems in thermodynamic equilibrium.For a system without chemical reactions, it relates the number of freely varying intensive properties (F) to the number of components (C), the number of phases (P), and number of ways of performing work on the system (N): [1] [2] [3]: 123–125

  5. Modal logic - Wikipedia

    en.wikipedia.org/wiki/Modal_logic

    One cannot prove in K that if "p is necessary" then p is true. The axiom T remedies this defect: T, Reflexivity Axiom: pp (If p is necessary, then p is the case.) T holds in most but not all modal logics. Zeman (1973) describes a few exceptions, such as S1 0. Other well-known elementary axioms are: 4:

  6. Surface tension - Wikipedia

    en.wikipedia.org/wiki/Surface_tension

    F w is the weight and F s are surface tension resultant forces. When an object is placed on a liquid, its weight F w depresses the surface, and if surface tension and downward force become equal then it is balanced by the surface tension forces on either side F s, which are each parallel to the water's surface at the points where it contacts ...

  7. Thermodynamic state - Wikipedia

    en.wikipedia.org/wiki/Thermodynamic_state

    Pressure (P) is the force exerted by the particles of a system on a unit area of the container walls. Volume ( V ) refers to the space occupied by the system. Composition defines the amount of each component present for systems with more than one component (e.g., mixtures).

  8. Triple point - Wikipedia

    en.wikipedia.org/wiki/Triple_point

    A typical phase diagram.The solid green line applies to most substances; the dashed green line gives the anomalous behavior of water. In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium. [1]

  9. State of matter - Wikipedia

    en.wikipedia.org/wiki/State_of_matter

    Matter in the liquid state maintains a fixed volume (assuming no change in temperature or air pressure), but has a variable shape that adapts to fit its container. Its particles are still close together but move freely. Matter in the gaseous state has both variable volume and shape, adapting both to fit its container.