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75 Cards in this Set
- Front
- Back
Newton's first law of motion
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Inertia
= Velocity of an object only changes when forces act on it |
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force
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something that can change an object's velocity
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speed of light
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2.998 x 10⁵ km/sec
~300,000 km/sec |
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light-year
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9.46 x 10^12 km
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parsec
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distance to nearest star
3.261633 light years |
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The Four Fundamental Forces
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strong force
weak force electromagnetic force gravitational force |
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strong force
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holds together nuclei of atoms
100 times stronger than electromagnetic force that repels protons 1 billion times stronger than weak force three colors combine to make neutral combinations "gluon" particle carries strong force |
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weak force
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causes one type of larger-mass particle to decay into another lower-mass kind of particle
a billion times weaker than strong force 10 million times weaker than electromagnetic force W and Z carrier particles |
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electromagnetic force
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opposites attract, likes repel
photon 100 times weaker than strong force 10 million times stronger than weak force |
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ecliptic
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line that sun traces across the celestial sphere
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celestial poles
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areas of sky right above earth's rotational poles - stars here do not move
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celestial equator
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line of sky along earth's equator
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vernal equinox
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march 21
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autumnal equinox
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sept 23
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solstices
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june 21
dec 21 |
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arctic circle
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north of 66.5 degrees N
sun does not rise during parts of the year |
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antarctic circle
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south of 66.5 degrees S
sun does not rise during parts of year |
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tropic of cancer
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23.5 degrees N
northern limit of "tropical" latitudes. sun is in the zodiac constellation Cancer at this latitude during summer solstice |
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tropic of capricorn
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23.5 degrees S
southern limit of "tropical" latitudes sun is in zodiac constellation capricorn during winter solstice |
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precession
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"wobbling" of spinning earth (think of a top)
happens very slowly - a single "wobble" takes 26,000 years |
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ante meridian
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a.m.
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post meridian
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p.m.
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sidereal day
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one day as measured by how long it takes a star to return to the same point in the sky
23 hours, 56 minutes, 4.0905 seconds |
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leap second
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adjustment of atomic clocks by a second every year or two to compensate for gradual slowing of earth's orbit
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tidal friction
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moon exerts gravity on ocean tides to make them more stationary than the earth's rotation generally -- tides 'run into' sides of continents and create friction with respect to rotation
this is gradually slowing the orbit of the earth -- 400 million years ago earth had 22 hours in a day, 400 days in a year. |
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solar eclipse
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moon passes between sun and earth, shadow of moon falls on earth
can only occur at new moon |
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lunar eclipse
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shadow of earth falls on moon
can only occur at full moon |
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umbra
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regions during an eclipse where light is blocked completely
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penumbra
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regions during an eclipse where light is only partially blocked
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annular eclipse
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moon is far enough away from earth at time of solar eclipse that it appears smaller than sun and one can see sun as a 'ring' around the moon during eclipse
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parallax
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shift in star's apparent position resulting from earth's motion round the sun
usually VERY SMALL |
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angular size
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how big an object *looks*
measured by drawing (imaginary) lines to each side of object and then measuring the angle linear size = distance x angular size/57.3 degrees |
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retrograde motion
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planets (like mars) appear to move backward in sky for a time because earth is orbiting faster than other planet
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Kepler's first law
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Planets move in elliptical orbits with the sun at one focus of the ellipse
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Kepler's second law
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orbital speed of a planet varies such that a line joining the sun and the planet will sweep over equal areas in equal time
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Kepler's third law
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the amount of time a planet takes to orbit the sun (P) is related to its orbit's size (a).
P^2 years= a^3 AU |
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mass
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amount of matter an object contains
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weight
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net force acting on an object (generally in a constant manner)
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acceleration
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change in velocity / change in time
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velocity
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directional speed
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Newton's second law of motion
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the force (F) acting on an object equals the product of its acceleration (a) and its mass (m).
F = m x a |
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Newton's third law of motion
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action-reaction
When two bodies interact, they create equal and opposite forces on each other |
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Newton's Universal Law of Gravitation
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Every mass exerts a force on every other mass.
This force (F) is proportional to the product of the masses (M x m) divided by the square of the distances between them. F = G x M x m / d^2 |
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newton
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kg x m / sec^2
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surface gravity
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Acceleration (g) caused by gravity on a planet's surface. Mass of falling object does not matter, acceleration will be the same.
g = G x M / R^2 |
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centripetal force
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Applied to any object moving in a circle or curve. Centripetal force (F) on an object with mass (m) moving with a velocity (V) at distance (d) from the cetner fo the circle...
F = m x V^2 / d Mass of an orbital center from the speed and distance of an object orbiting it... M = d x V^2 / G |
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Newton's modification of Kepler's Third Law
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Sum of masses of two orbiting bodies (M(a) and M(b)) obey the following law (where masses are in units of the mass of the sun)...
M(a) + M(b) = a^3 AU / P^2 years |
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orbital velocity
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object in scircular orbit must have velocity of...
V = (G x M / R)^(1/2) |
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escape velocity
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velocity needed to escape from the gravitational pull of a body
V = (2GM/R)^(1/2) |
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tidal bulges
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differential gravitational forces pull water into bulges on side of earth facing the moon as well as on side directly opposite
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kinetic energy
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energy of an object in motion
E = 1/2 x m x V^2 E in joules m in kg V in m/sec |
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gravitational potential energy
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E = (-G x m x M)/d
E in joules m, M in kg d in m |
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Angular momentum
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inertia applied to rotation, unless acted upon by an outside rotational force (torque)
If a mass (m) is moving around a rotational axis at a distance (r) with a velocity (V), then it's angular momentum... = m x V x R |
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"quantized" energy
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comes in discrete packets
e.g., you can have 1, 2, or 3 photons, but not 1/2 or 1.7 |
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inverse-square law
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brightness = total light output / (4πd^2)
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emission
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electron drops from a higher to a lower orbital and gives off energy of a specific amount as an electromagnetic wave
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absorption
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light's energy is stored in an atom as energy, moving an electron to a higher orbital
Absorption can ionize an atom if the energy given to the electron is great enough that it escapes the orbit of the atom completely. |
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wavelength
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spacing between wave crests according to wave interpretation of light
Usually represented by Greek letter λ. |
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Frequency
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number of wave crests that pass a point in 1 second
This unit is hertz (Hz) Usually denoted by Greek letter nu: ν |
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relation of frequency to wavelength
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by definition...
λ x ν = c |
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energy carried by photons
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A photon carries an amount of energy proportional to its frequency and inversely proportional to its wavelength
E = (h x c) / λ h = Planck's constant |
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blackbody
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an object that absorbs all radiation falling on it
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Wien's Law
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Hotter bodies radiate more strongly at shorter wavelengths
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Stefan-Boltzmann Law
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The luminosity of a hot body rises rapidly with temperature.
Luminosity is proportional to temp (in degrees Kelvin) to the fourth power luminosity ~ T^4 |
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continuous spectrum
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atoms emit light of all visible wavelengths
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emission-line spectrum
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produced by hot, low-density gas
molecules well-separated so atoms can become excited without bumping into each other too much, thus they produce specific emissions when they drop back down |
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absorption-line spectrum
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light from a hot, dense body (like sun) passes through cooler gas between it and observer
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radial velocity
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speed of an object along one line of sight:
V = (Δλ / λ) x c This uses Doppler shift, where λ is the wavelength originally generated |
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CCDs
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charge-coupled devices
Superior, reusable alternative to film. Gets about 75% efficiency of photon recording as opposed to film's ~10% |
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collecting area
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the bigger a telescope's collecting area, the more photons it can gather
The area of a circular collector of diameter D is... Collecting area = (π/4) x D^2 |
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refraction
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transparent lenses bend electromagnetic waves including light
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dispersion
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different wavelengths of light refracted at different amounts, like white light passing through a prism
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diffraction
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when waves pass thru an opening, they are bent at the edges of the opening
relevant for telescope-making |
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calculating resolution of a telescope
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D(cm) > 0.02λ(nm) / α (arcsec)
or α > 0.02λ / D |
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interferometer
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combined set of telescopes that function like one big telescope
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