Phyics: Modules 1,2,& 3

My revision notes for physics. Remember, always check the back page!

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  • Created on: 02-01-11 15:06
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PHYSICS REVISION
P1- THE EARTH IN THE UNIVERSE
Rocks provide evidence for changes to the earth (erosion and sedimentation, fossils, folding,
radioactive dating, craters)
Continents would be worn down to sea level if mountains were not being constantly formed. Rocks
are constantly changing and being recycled. Erosions + lava from volcanoes set. Fossils and this
provide evidence that rocks are constantly forming.
The rock cycle- is recycling rocks. Particles from erosion get washed into the sea and settle as
sediment. Over time this crushes together to get sedimentary rocks then either it is pushed to the
surface or it descends into heat + pressure inside the earth. the structure of the rock changes
when heated or crushed sometimes the rock melts, but solidifies to new rock cycle starts again.
It needs powerful forces to push the rock.
Rock processes seen today can account for past changes. Looking at proportions of radioactive
potassium-40 in rocks, with this, scientists can work out when they were formed.
The oldest rocks on earth are approximately 4 thousand billion years old so earth must be at
least that old.
Centre of earth is an iron and nickel core, them the mantle- properties of a solid, but can flow very
slowly- radioactive takes place, produces a lot of heat, causing the mantle to flow convection
currents, then the crust- a very thin (about 20km) continental or oceanic.
The solar system was formed over very long periods from clouds of gases and dust in space, about 5
thousand million years ago.
Things in the Solar System- in order of size: Sun- huge-diameter100xbigger earth, gives out
light
Planets- smaller, reflect light-much closer moons orbiting them- Jupiter has 63
Moons- Orbit Planets
Asteroids- smallish lumps of rubble and rock- and Comets- balls of rock, dust and
ice, which orbit the sun. As the comet approaches the sun, the ice melts + leaves a bright tail
of gas + debris, can be millions of km long.
The fusion of hydrogen nuclei is the source of the sun's energy
All chemical elements larger than helium were made in earlier stars
Particles of dust or small rocks (asteroids) often enter the earth's atmosphere. They usually
burn up, so we see `shooting stars'. Very rarely they hit earth, causing havoc- they could: cause
tsunamis, start fires (if they go on land and throw hot rocks and dust into the earth), dust and smoke
can block out sunlight for months, causing climate change, causing species to be extinct, big holes in
ground, craters.

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The extinction of the dinosaurs- 65 million years ago- could be asteroid collision (but dinosaurs
died before this) or volcano eruption (layers of basalt in India- but basalt in N-Ireland- no extinction
there
Light travels at a high but finite speed- 300,000 km/s- speed of light- distance travelled by light in a
year means that distant objects are observed as younger than they are now- closest star to us is 4.2
light years away.…read more

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All stars have a life cycle (learn?)
Astronomers have detected planets around some nearby stars
Even if a small proportion of stars have planets, many scientists think that it is likely that life exits
somewhere else in the universe- there is no evidence of alien life.
Distant galaxies are moving away from us ­ the galaxies that are more distant are moving away
faster than closer ones.…read more

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Radiation sickness is when you are exposed to high levels, it can kill your cells
altogether.
UV radiation from the sun is ionising can cause damage to cells in the skin. Sun burn and skin cancer.
The metal cases and door screens of microwave ovens protect users from the radiation.
Physical barriers protect people from ionising radiation eg. Sun screens, clothing and the ozone
absorbs UV, and lead shields for X-Rays lead aprons for radiographer.…read more

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Gamma- stopped by thick lead- type of EM radiation (no mass) can penetrate a long way, just
energy, so it doesn't change the element of the nucleus that emits it. Get rid of extra energy, can
irradiate surgical instruments and track the movement of chemical inside the body
Over time, the activity of radioactive sources decreases.
Half life- the time for the activity to fall to half its initial energy
Radioactive elements have a wide range of half life values.…read more

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Compare the amount of energy released during a nuclear fission to that released in a chemical
reaction...
The nuclear fission process in nuclear power stations is controlled: .... terms: chain reaction, fuel
rod, control rod and coolant
Nuclear power stations produce radioactive waste.…read more

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