AQA GCSE Physics

Revision Notes

8.1.2 The Formation of the Sun

The Formation of the Sun

  • The Sun is formed from massive clouds of dust and gas in space
    • A cloud of dust and gas in space is called a nebula

Nebula, downloadable IGCSE & GCSE Physics revision notes

A nebula is a cloud of gas and dust in space (Image courtesy of NASA)

  • Gravity pulled this cloud together into a giant ball

protoplanetary-disk, IGCSE & GCSE Physics revision notes

The nebula collapses due to gravity and begins to rotate (Image courtesy of NASA)

  • As the nebula collapsed the centre of this ball got very dense and hot and began to rotate
  • Eventually nuclear fusion  was able to begin and a dense protostar was formed – our Sun

The Sun, downloadable IGCSE & GCSE Physics revision notes

Our Sun (Image courtesy of NASA)

Equilibrium in Stars

  • Stars are held together by a delicate balance of inwards and outwards forces
  • One of these forces is the force of gravity
    • This is an attractive force which pulls the outer layers inwards
  • The other force is the force of pressure
    • This is an outward force which is exerted from the expanding hot gases inside the star

Equilibrium in Stars

  • When the inward pull of gravity and the outward pressure acting on the star are equal the star will be in equilibrium

hydrostatic-equilibrium, IGCSE & GCSE Physics revision notes

Forces acting within a star. The centre red circle represents the star’s core and the orange circle represents the stars outer layers

  • If the temperature of a star increases, the outward pressure will also increase
    • This will cause the star to expand
  • If the temperature drops (because, perhaps, the rate of fusion has slowed) the outward pressure will also decrease
    • This will cause the star to contract

Author: Katie

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.
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