Full notes for the 2 Physics papers under the Triple Science course, going over:
-All topics that can come up in both papers
-Any required practicals linked to this
-Key words and definitions
-Equations and formulae
P1.1 What do we know about the place of the Earth in the Universe?
The Earth is one of eight planets orbiting the sun in almost circular paths, together with other
smaller objects including asteroids, dwarf planets, comets and moons. The solar system is made.
The smaller masses in our solar system are:
Planets – eight large masses that orbit (move around the sun)
Moons – small masses that orbit the planets
Asteroids – small, rocky masses that orbit the Sun
Comets – small, icy masses that orbit the sun
Dwarf planets – small spherical objects that have not cleared their orbits of other objects
The solar system was formed over a very long period of time, about 5000 million years ago:
❶ The solar system started as clouds of DUST and GAS, which were pulled together by the force of
gravity
❷ This created intense heat. Eventually, NUCLEAR FUSION began to take place and a star was born:
the Sun
❸ The remaining dust and gas formed smaller masses, which were attracted to the sun
Our sun is one of thousands of millions of stars which form the Milky Way. There are thousands of
millions of galaxies and every galaxy is made up of thousands of millions of stars – all these galaxies
make up the UNIVERSE.
SMALLEST Diameter of the Earth
Diameter of the Sun
Diameter of the Earth’s orbit
Diameter of the Solar system
Distance from the Sun to the nearest star
Diameter of the Milky way
LARGEST Distance from the Milky way to the nearest galaxy
Because stars are so far away, all the evidence we have about distant stars and galaxies come from
the RADIATION astronomers can detect. A lot is shown when studying the ELECTROMAGNETIC
RADIATION it emits – e.g. the colour the star appears shows its surface temperature.
,Light travels at very high but FINITE (limited) speeds. This means that if the distance to an object is
great enough, the time taken for light to get there can be measured.
The speed of light is 300,000km/s in a vacuum.
Vast distances in space are measured in LIGHT YEARS. One light year is the year is the distance light
travels in one year (approximately 9500 billion km). 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. the nearest galaxy to the Milky Way is 2.2 million light-years away. This means that light from
this galaxy has taken 2.2 million years to reach the Earth, and so we are now seeing the galaxy as it
was in the past.
Astronomers work out the distances to different STARS using two different methods:
❶ Relative brightness
In general, the dimmer a star is, the further away it is. However, stars can vary in brightness so we
can never be 100% certain
❷ Parallax
Parallax is when something appears to move when you look at it from different places (e.g. if you
hold your finger at arm’s length and close each eye in turn the finger appears to move. The closer
the finger is to your face, the more it appears to move).
As the Earth orbits the Sun, stars in the
near distance appear to move against the
background of very distant star. The closer
they are, the more they appear to move.
The position of a star is measured at six-
monthly intervals. These measurements
can then be used to calculate its distance
from Earth.
However the further away the star is, the
more difficult and less accurate the
measurement is.
In the last 200 years, it has become very difficult to make astronomical observations in
INDUSTRIALISED COUNTRIES such as the UK. This is due to the bright lights found in cities and towns
and on roads. This LIGHT POLLUTION means it is hard to see dim stars.
Also the Earth’s ATMOSPHERE absorbs quite a bit of the light coming from space before it can reach
us.
This is why scientists put the HUBBLE SPACE TELESCOPE in space – where you don’t get these
problems.
,The sun’s energy (heat and light) comes from NUCLEAR FUSION. Hydrogen nuclei fuse (join)
together to produce a nucleus with a larger mass, i.e. a new chemical element.
During fusion, some of the energy trapped inside the hydrogen nuclei is released. All the chemical
elements with a larger mass than helium were formed by nuclear fusion in earlier stars.
When a galaxy is moving away from us the WAVELENGTH of the light from it changes – the light
becomes redder. This is called RED SHIFT:
By seeing how much the light has been red-shifted, you can work out how quickly it’s moving away.
The greater the red-shift the faster it’s moving away. From the observations of different red-shifts of
different galaxies we know that:
The more DISTANT the galaxy, the FASTER it moves away from us
This provides evidence that the whole universe is EXPANDING.
Different stuff in the universe Age (million years)
Earth 5000
Sun 5000
Universe 14 000
The Earth and the sun are a similar age. But the universe is about 3x older.
When Scientists trace the paths of galaxies, they all appear to be moving away from the same point.
The best theory for this is the BIG BANG THEORY, which says that the universe started with a huge
explosion 14,000 million years ago.
The ultimate fate of the Universe this is because the future depends on the amount of MASS in the
Universe.
If there is NOT ENOUGH MASS, the universe will keep expanding
If there is TOO MUCH MASS, gravity will be strong enough to pull everything back together and the
universe will collapse with a big crunch.
Measuring the amount of mass in the Universe is very difficult, so it’s ultimate fate.
, P1.2 What do we know about the Earth and how it is changing?
Rocks provide evidence for changes in the Earth:
Erosion – the Earth’s surface is made up of LAYERS of rock, one on top of the other with the
oldest at the bottom. The layers are made of compacted SEDIMENT, which is produced by
weathering and EROSION. Erosion changes the surface of the planet over long periods of
time.
Fossils – plants and animals trapped in layers of sedimentary rock have formed FOSSILS,
providing evidence of how life on Earth has changed over millions of years.
Folding – some rocks look as if they have been
FOLDED like plasticine. This would require a big force
to be applied over a long period of time – further
evidence that the Earth is very old.
Mountain formation – if MOUNTAINS were not
being formed, the whole Earth would have been
worn down to sea level by erosion.
Rock processes seen today can account for past changes.
Scientists estimate that the Earth is around 4500 million years old – it has to be older than its oldest
rocks - and when it was first formed it was completely molten (hot liquid) and would have taken a
very long time to cool down. The oldest rocks that have been found on Earth are about 4500 million
years old.
The age of the Earth must be greater than the age of it oldest rocks.
Alfred Wegner (1880-1930) was a meteorologist who put forward a theory called CONTINENTAL
DRIFT. He saw that the continents fitted together like a jigsaw, with the MOUNTAIN RANGES and
SEDIMENTARY ROCK patterns matching up almost perfectly. There were also FOSSILS of the same
land animals on different continents. Wegner proposed that the different continents were once
joined together but had become separated and drifted apart.
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