Physics P1 Revision sheet


Physics  (P1):

The Earth in the Universe-


General facts:-

·         There are eight planets orbiting the sun in ellipses.

·         Closest to the sun are the inner planets – Mercury, Venus, Earth and Mars. Then there is the asteroid belt and then the outer planets – Jupiter, Saturn, Uranus and Neptune.

·         There are also various other things such as, dwarf planets, comets, dust and so on... which are all in the orbit around the sun. Planets often have moons orbiting them, which are usually much smaller and found close to the planet. These also count as part of the solar system.

·         Stars and planets are very different from eachother.

·         Stars are huge (the sun’s diameter is over 100 times bigger than the Earth’s), very hot , very far away and they give out lots of light.

·         Planets are smaller and reflect the light falling on them. The planets in the solar system are also much closer to us then any star (except for the sun).


The Solar system:-

·         The solar system is approximately 5 thousand million years old.

·         The solar system was formed over a  long period of time by big clouds of dust and gas.

·         For some reason (maybe a nearby star exploding), one cloud started to get squeezed slightly.

·         Once the particles had moved a bit closer together, gravity took over.

·         It pulled things closer and closer together until the whole cloud started to collapse in on itself.

·         At the centre of the collapse, particles came together to form a protostar. When the temperature got high enough, a process called fusion started – hydrogen nuclei joined together to make helium.

·         Fusion gives out massive amounts of heat and light, so a star... our sun was born. The sun and other stars’ energy comes from the fusion of hydrogen nuclei.

·         All of the chemical elements in the clouds with heavier atoms then helium and hydrogen were also formed in the stars by the fusion of different nuclei.

·         Around the sun, material from the cloud containing hydrogen, helium and heavier elements started to clump together and these clumps became planets. (So the sun and planets are similar ages).

·         The oldest rocks on Earth are actually meteorites. These are around 4500 million years old.



Asteroids and comets:

-          These are much smaller than most planets.

-          They are both made up from stuff left over from the formation of the solar system.

-          Asteroids are small lumps of rubble and rock.

-          Comets are balls of ice, rock and dust, which orbit the sun in very elongated ellipses, often in different planes from the planets. The sun is near one end of the orbit.

-          As a comet approaches the sun, its ice melts, leaving a bright tail of gas


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