Реферат: Физические законы, переменные, принципы
Grandfather paradox
A paradox proposed to discount time travel and show why itviolates causality. Say that your grandfather builds a timemachine. In the present, you use his time machine to go back intime a few decades to a point before he married his wife (yourgrandmother). You meet him to talk about things, and an argumentensues (presumably he doesn't believe that you're hisgrandson/granddaughter), and you accidentally kill him.
If he died before he met your grandmother and never hadchildren, then your parents could certainly never have met (one ofthem didn't exist!) and could never have given birth to you. Inaddition, if he didn't live to build his time machine, what areyou doing here in the past alive and with a time machine, if youwere never born and it was never built?
Hall effect
When charged particles flow through a tube which has both anelectric field and a magnetic field (perpendicular to the electricfield) present in it, only certain velocities of the chargedparticles are preferred, and will make it undeviated through thetube; the rest will be deflected into the sides. This effect isexploited in such devices as the mass spectrometer and in theThompson experiment. This is called the Hall effect.
Hawking radiation (S.W. Hawking; 1973)
The theory that black holes emit radiation like any other hotbody. Virtual particle-antiparticle pairs are constantly beingcreated in supposedly empty space. Every once in a while, onewill be created in the vicinity of a black hole's event horizon.One of these particles might be catpured by the black hole,forever trapped, while the other might escape the black hole'sgravity. The trapped particle, which would have negative energy(by definition), would reduce the mass of the black hole, and theparticle which escaped would have positive energy. Thus, from adistant, one would see the black hole's mass decrease and aparticle escape the vicinity; it would appear as if the black holewere emitting radiation. The rate of emission has a negativerelationship with the mass of the black hole; massive black holesemit radiation relatively slowly, while smaller black holes emitradiation -- and thus decrease their mass -- more rapidly.
Heisenberg uncertainty principle (W. Heisenberg; 1927)
A principle, central to quantum mechanics, which states that themomentum (mass times velocity) and the position of a particlecannot both be known to infinite accuracy; the more you know aboutone, the lest you know about the other.
It can be illustrated in a fairly clear way as follows: Tosee something (let's say an electron), we have to fire photons atit, so they bounce off and come back to us, so we can "see" it.If you choose low-frequency photons, with a low energy, they donot impart much momentum to the electron, but they give you a veryfuzzy picture, so you have a higher uncertainty in position sothat you can have a higher certainty in momentum. On the otherhand, if you were to fire very high-energy photons (x-rays orgammas) at the electron, they would give you a very clear pictureof where the electron is (high certainty in position), but wouldimpart a great deal of momentum to the electron (higheruncertainty in momentum). In a more generalized sense, the uncertainty principle tellsus that the act of observing changes the observed in fundamentalway.
Hooke's law (R. Hooke)
The stress applied to any solid is proportional to the strain itproduces within the elastic limit for that solid. The constant ofthat proportionality is the Young modulus of elasticity for thatsubstance.
Hubble constant; H0 (E.P. Hubble; 1925)
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Hubble's law (E.P. Hubble; 1925)
A relationship discovered between distance and radial velocity.The further away a galaxy is away from is, the faster it isreceding away from us. The constant of proportionality isHubble's constant, H0 . The cause is interpreted as the expansionof space itself.
Huygens' construction; Huygens' principle (C. Huygens)
The mechanics propagation of a wave of light is equivalent toassuming that every point on the wavefront acts as point source ofwave emission.
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The constant that appears in the ideal gas equation. It is equalto 8.314 34.
Ideal gas equation
An equation which sums up the ideal gas laws in one simpleequation. It states that the product of the pressure and thevolume of a sample of ideal gas is equal to the product of theamount of gas present, the temperature of the sample, and theideal gas constant.
Ideal gas laws
Boyle's law. The pressure of an ideal gas is inversely proportional to the volume of the gas at constant temperature.