AQA GCSE Physics (8463) · Paper 2
🚀 Space Physics
Revision notes written to the specification, with examiner tips and the required practicals. Every point here has flashcards in the Stickwise app.
Stars & the solar system (Triple) Separate science only
Our solar system consists of the Sun, eight planets, dwarf planets such as Pluto, and moons, which are natural satellites orbiting planets. It is just one system among billions in the Milky Way galaxy.
The Sun formed when a cloud of dust and gas, called a nebula, collapsed under gravity to form a protostar. Its core grew hot and dense enough to ignite the fusion of hydrogen into helium. A main sequence star is stable because the outward pressure produced by fusion exactly balances the inward pull of gravity, and this balance can last for billions of years.
Nuclear fusion in stars builds up elements as heavy as iron. Elements heavier than iron are only formed during a supernova, a huge stellar explosion, which then scatters these elements through space. The material that makes up new stars, planets and living things originally came from earlier generations of stars.
Orbits & the expanding universe (Triple) Separate science only
Gravity supplies the force needed for every orbit, including planets orbiting the Sun and moons and satellites orbiting planets.
Higher content: in a circular orbit the speed stays constant but the velocity is constantly changing, because the direction of motion keeps changing, so the orbiting body is always accelerating towards the centre of the orbit. If the speed changes, the radius of the orbit must change as well.
Red-shift and the Big Bang
Light from distant galaxies is stretched to longer wavelengths, shifting it towards the red end of the spectrum; this effect is called red-shift. The further away a galaxy is, the bigger its red-shift, which means the most distant galaxies are moving away from us the fastest. This shows that the whole universe is expanding.
If the expansion of the universe is run backwards, everything began at one tiny, hot, dense point, an event called the Big Bang, which happened around 13.8 billion years ago. Red-shift is the main evidence for this theory.
Since 1998, observations have shown that the expansion of the universe is speeding up, and galaxies rotate as if they contain far more mass than can be seen. Dark energy and dark matter are the names given to whatever is causing these effects; together they make up most of the universe, but what they actually are is not yet understood. This remains an active area of scientific research.