ESS
Grade-9
Easy
Question
The ______ and ___________balance and keep a main sequence star in equilibrium.
- Gravity and friction
- Gravity and air quality
- Gravity and radiation pressure
- None of these
Hint:
In the main sequence the star remains constant in size despite the outward energy flow.
The correct answer is: Gravity and radiation pressure
- In the Main Sequence Phase of a star's evolution, radiation pressure pushing outward exactly balances the gravitational pressure pulling inward (this balance is called Hydrostatic Equilibrium).
- Because these two forces are exactly in balance, the star is stable (this means it neither shrinks nor expands).
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