Module 3 Definitions Flashcards
Thermal equilibrium
A state in which there is no net flow of thermal energy between objects. Objects must have the same temperature
Triple point
One specific temperature and pressure at which all three phases of a substance exist in thermal equilibrium
Celsius scale
A temperature scale with 100 degrees between the freezing point and boiling point of water.
Absolute zero
The lowest possible temperature.
Brownian motion
The continuous random motion of small particles suspended in a fluid visible under a microscope
Internal energy
The sum of randomly distributed kinetic and potential energies of the atoms, ions or molecules in a substance.
Specific heat capacity
The energy required per unit mass to change the temperature by 1k.
Specific latent heat
The energy required to change the phase per unit mass while at a constant temperature
Specific heat of fusion
The energy required to change unit mass of a substance from solid to liquid while at a constant temperature
Specific latent heat of vaporisation
The energy required to change unit mass of a substance from liquid to gas while at a constant temperature
Maxwell Boltzmann distribution
The distribution of all the speeds of particles in a gas
Angular velocity
The rate of change of angle for an object moving in a circular path
Centripetal force
A force that keeps a body moving with a constant speed in a circular path
Centripetal acceleration
The acceleration of any object travelling in a circular path at constant speed which always acts towards the centre of the circle.
Isochronous oscillator
An oscillator that has the same period regardless of the amplitude
Simple harmonic motion
Oscillating motion for which acceleration of an object is directly proportional to the displacement and is directed toward some fixed point
Light damping
Damping that occurs when the damping forces are small and the period of the oscillation is almost unchanged
Damping
An oscillation is damped when an external force that acts on the oscillator has the effect of reducing the amplitude of its oscillations
Free oscillation
The motion of a mechanical system displaced from its equilibrium position and then allowed to oscillate without any external forces
Natural frequency
The frequency of free oscillation
Forced oscillation
An oscillation in which a periodic driver force is applied to an oscillator
Driving frequency
The frequency with which a periodic driver force is applied to a system in a forced oscillator
Resonance
The increase in amplitude of a forced oscillation when the driving frequency matched the natural frequency of the oscillating sustem.
Gravitational field
A field created around any object with mass, extending all the way to infinity but diminishing as the distance from the centre of mass of object increases
Gravitational field strength
The gravitational force exerted per unit mass at a point within a gravitational field
Uniform gravitational field
A gravitation field in which the field lines are parallel and the value for g remains constant
Newtons law of gravitation
The force between two point masses is directly proportional to the product of the mass and inversely proportional to the square of the separation between them.
Kelpers first law
The orbit of a planet is an ellipse with the sun at one of the two foci.
Ellipse
An elongated circle with two foci
Eccentricity
A measure of the elongation of an ellipse
Aphelion
The furthest point from the sun in an orbit
Perihelion
The closest point to the sun in an orbit.
Keplers second law
A line segment connecting a planet to the sun sweeps out equal area during equal intervals of time.
Keplers third law
The square of the orbital period of a planet is directly proportional to the cube of its average distance r from the sun.
Astronomical unit
The mean distance from earth to the sun
Geostationary satellites
A satellite that remains in the same position relative to a spot on the earth’s surface, by orbiting in the direction of the earths rotation over the equator with a period of 24 hours.
Gravitational potential
The work done per unit mass to bring an object from Infinity to a point in the gravitation field
Escape velocity
The minimum velocity at which an object has just enough energy to leave a specified gravitational field.
Nebula
A cloud of dust and gas (mainly hydrogen), often may hundreds of times larger than our solar system.
Protostar
A very hot, denser sphere of condensing dust and gas that is on the way to becoming a star
Nuclear fusion
A process in which two smaller nuclei join together to form one larger nucleus.
Radiation pressure
Pressure from the photons in the core of a star,which acts outwards to counteract the pressure from the gravitational force pulling the matter in the star inwards.
Gas pressure
In stars, the pressure of the nuclei in the star’s core pushing outwards and counteracting the gravitational force pushing the matter in the star inwards
Main sequence star
The main period in a star’s life during which it is stable.
Red supergiant
A huge star in the last stages of its life before it explodes in a supernova
Supernova
The implosion of a red supergiant at the end of its life which lead to subsequent ejection of stellar matter into space leaving an inert remnant core.
Red giant
An expanding star at the end of its life, with an inert core in which fusion no loners takes place, but in which fusion of lighter elements in the shell around the core.
Planetary nebula
The outer layers of a red giant that has drifted into space leaving the hot core behind at the centre as a white dwarf.
White dwarf
A very dense star formed from the core of a red guant in which no fusion occurs
Electron degeneracy pressure
A quantum mechanical pressure created by the electrons in the core of a collapsing star due to the Pauli exclusion principle.
Chandrasekhar limit
The mass of a star’s core beneath which the electron deneracy pressure is sufficient to prevent gravitational collapse. 1.4c solar masses.
Neutron star
The remnant core of a massive star after the star has gone supernova and (if the mass of the core is greater then the Chandrasekhar limit) the core has collapsed under gravity to an extremely high density, as it is almost entirely made up of neutrons.
Black hole
The remnant core of a massive star after it has gone supernova and the core has collapsed so far that in order to escape it an object would need an escape velocity greater than the speed of light, and therefore nothing, not even a photon can escape it.
Hetzsprung russell diagram
A graph showing the relationship between the luminosity of star in our galaxy and the average surface
Luminosity
The total radiant power output of a star.
Energy levels
A discrete amount of energy that an electron within an atom is permitted to possess.
Ground state
The energy level with the most negative value possible for an electron within an atom- the most stable energy state of an electron.
Emission spectra
A set of specific frequencies of electromagnetic radiation, visible as bright lines in spectroscopy, emitted by excited atoms as their electrons transition between higher and lower energy states, losing the corresponding amount of energy in the form of photons. Every element has a characteristic line spectrum.
Grating spacing
The separation between adjacent lines or slit in a diffraction grating.
Black body
An idealised object that absorbs all the electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution of wavelengths at a specific temperature.
Wien’s displacement law
The peak wavelength at which the intensity of radiation from a black body is a maximum is inversely proportional to the absolute temperature of the black body.
Cosmological principle
The Universe is homogeneous and isotopic and the laws of physics are universal.
Blue shift
The shortening of observed wavelength that occurs when a wave source is moving toward the observer. If a galaxy is moving towards the earth, the absorption lines in its spectrum will be blue shifted to is moved towards the blue end of the spectrum.
Red shifted
The lengthening of observed wavelength that occurs when a wave source is moving away from the observer. If a galaxy is moving away from earth, the absorption lines in its spectrum will be shifted towards the red.
Doppler effect
The change in the frequency and wavelength of waves received from a moving relative to an observer compared with what would be observed without relative motion.
Big bang
The theory that at a moment in the past all the matter in the universe was contained in a single point , the beginning of so we and time, that expanded rapidly outwards.
Hubbles law
The recessional speed of a galaxy is directly proportional to its distance from the earth.
Homogeneous
Uniform in terms of the distribution of matter across the Universe when viewed on a sufficiently large scale.
Isotropic
The same in all directions
Eg. The universe appearing the same to any observer regardless of the position
Microwave background radiation
The microwave signal of uniform intensity detected from all directions of the sky, which fits the profile for a black body at a temperature of 2.7k.
Dark energy
A hypothetical from of energy that fills all of space and would explain the accelerating expansion of the universe.
Dark matter
A hypothetical form of matter spread through the galaxy that neither meets or absorbs light.
Zeroth law
If two objects are each in thermal equilibrium with a third then all three are in thermal equilibrium with each other.
