P1 Revision Notes

Página 1

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The Earth is one of eight planets moving in

almost circular paths round the Sun which, together with other smaller objects

orbiting the Sun (asteroids, dwarf planets, comets) and moons orbiting several

planets, make up the solar system.

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The solar system was formed over very long

periods from clouds of gases and dust in space, about five billion years ago.

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The Sun is one of thousands of millions of stars

in the Milky Way galaxy

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There are thousands of millions of galaxies,

each containing thousands of millions of stars, and all of these galaxies make

up the Universe.

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All the evidence we have about distant stars and

galaxies comes from the radiation astronomers can detect.

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Light travels through space (a vacuum) at a very

high but finite speed, 300 000 km/s

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A light-year is the distance travelled by light

in a year.

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The finite speed of light means that very

distant objects are observed as they were in the past, when the light we now

see left them (e.g. we see the sun 8 mins after the light left it, and the

nearest stars 2-5 years later).

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Parallax method to measure distance to a star - The

star is observed against a background of distant stars, then again six months

later. The star appears to move against the background. The bigger the apparent

movement, the nearer the star is to Earth.

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The brighter a star, the closer it is to Earth.

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Light pollution and other atmospheric conditions

interfere with observations of the night sky.

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The source of the Sun’s energy is the fusion of

hydrogen nuclei into helium.

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All chemical elements with atoms heavier than

helium were made in stars.

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The red shift in the light coming from them

suggests that distant galaxies are moving away from us

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The further away a galaxy is, the faster it is

moving away from us.

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The motions of galaxies suggests that space

itself is expanding.

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Universe is 14 billion years old, Sun and Earth

are 4.6 billion.

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Scientists believe the Universe began with a

‘big bang’.

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The ultimate fate of the Universe is difficult

to predict because of difficulties in measuring the very large distances

involved and the mass of the Universe, and studying the motion of very distant

objects.

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Rocks provide evidence for changes in the Earth

(erosion and sedimentation, fossils, folding).

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Continents would be worn down to sea level by

erosion, if mountains were not being continuously formed.

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The age of the Earth can be estimated from, and

must be greater than, the age of its oldest rocks, which are about four

thousand million years old.

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Wegener’s theory of continental drift –

geometric fit of continents and their matching fossils and rock layers).

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Wegener’s theory accounts for mountain building.

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Reasons for the rejection of Wegener’s theory by

geologists of his time (movement of continents not detectable, too big an idea

from limited evidence, simpler explanations of the same evidence, Wegener an

outsider to the community of geologists)

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Sea floor spreading is a consequence of movement

of the mantle (convection due to heating by the core).

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Sea floors spread by a few centimetres a year

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Sea floor spreading and the periodic reversals

of the Earth’s magnetic field can explain the pattern in the magnetisation of

sea floor rocks on either side of the oceanic ridges

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Earthquakes, volcanoes and mountain building

generally occur at the edges of tectonic plates

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The movement of tectonic plates causes

earthquakes, volcanoes and mountain building, and contributes to the rock cycle.

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Earthquakes produce wave motions on the surface

and inside the Earth which can be detected by instruments located on the

Earth’s

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Earthquakes produce:

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a) P-waves (longitudinal waves) which travel

through solids and liquids.

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b) S-waves (transverse waves) which travel

through solids but not liquids.

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Differences in the wave speeds and behaviour of

P-waves and S-waves can be used to give evidence for the structure of the Earth

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Distance = wave speed × time

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distance in metres m, speed in metres per second

m/s and time in seconds s

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Core, then mantle, then crust of Earth.

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A wave is a disturbance, caused by a vibrating source

that transfers energy in the direction that the wave travels, without

transferring matter.

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The frequency of waves, in hertz (Hz), is the

number of waves each second that are made by the source, or that pass through

any particular point.

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The wavelength of waves is the distance between

the corresponding points on two adjacent cycles.

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The amplitude of a wave is the distance from the

maximum displacement to the undisturbed position.

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Wave speed (m/s) =

frequency (Hz) × wavelength (m)

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For a constant wave speed the wavelength of the

wave is inversely proportional to the frequency.