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Equilibrium in Stars (Edexcel GCSE Physics)
Revision Note
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 from the pressure caused by the thermal expansion
- This is an outward force which is exerted from the expanding hot gases inside the star
- When the inward pull of gravity and the force from the outward thermal expansion acting on the star are equal, the star will be in equilibrium
- This is how the stars in the main sequence remain stable for millions of years
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 the outward pressure will also decrease
- This will cause the star to contract
- As long as these two forces balance, the star will remain stable
- Once these forces are unbalanced, then they will no longer be in equilibrium causing the star to expand or contract
- This happens when fusion in the core of stars, and hence thermal expansion, ceases at the end of the star's life
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