OCR · GCSE · Physics
Course version: J249 · Version from Sept 2018
Recall that our Sun was formed from dust and gas drawn together by gravity…
Full specification wording
Beyond Earth: recall that our Sun was formed from dust and gas drawn together by gravity and explain how this caused fusion reactions, leading to equilibrium between gravitational collapse and expansion due to the energy released during fusion (to include: lifecycle of a star) (content found only in the physics separate science qualification)
A cloud of dust and gas (a nebula) is pulled together by gravity.
Checked against the OCR J249 specification (opens in a new tab) on .
- Point 3 of 8
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A cloud of dust and gas (a nebula) is pulled together by gravity. As the material falls inward, gravitational potential energy becomes thermal energy, so the core heats up. When the core is hot enough, hydrogen nuclei fuse to form helium, releasing energy. That energy raises the pressure and pushes outward, while gravity pulls inward. When the two balance, the star is in equilibrium and stays stable for a long time. The Sun formed this way. In the wider lifecycle, a star of the Sun's mass later expands into a red giant, sheds its outer layers and leaves a white dwarf; more massive stars may end as neutron stars or black holes.
What earns the marks
- States that the Sun formed from dust and gas drawn together by gravity.
- Explains that gravitational collapse heats the core until hydrogen fusion begins.
- Describes equilibrium as a balance between inward gravitational collapse and outward pressure from energy released in fusion.
- Identifies that the Sun is a main-sequence star and outlines later stages such as red giant and white dwarf.
Common mistakes and how to put them right
Claims that fusion causes the cloud to collapse.
Put it right by stating that gravity causes the collapse and fusion releases the outward energy.
Describes equilibrium as the star no longer producing energy.
Put it right by stating that fusion continues and balances the inward pull.
Gives the Sun's endpoint as a black hole.
Put it right by stating that a Sun-like star ends as a white dwarf.
Exam tips
- Link each stage to the force or energy involved: gravity inward, fusion energy outward.
- Use the word equilibrium and state what is balanced.
- Keep the lifecycle sequence in order: nebula, main sequence, red giant, white dwarf.
Try the lesson
The start of the Beyond Earth: recall that our Sun was formed from dust and gas drawn together by gravity and explain how this caused fusion reactions, leading to equilibrium between gravitational collapse and expansion due to the energy released during fusion (to include: lifecycle of a star) (content found only in the physics separate science qualification) lesson, made from checked teaching notes for this specification point.
Have a go first
According to the accepted model, what did the material that formed our Sun originally consist of?
Listen
A cloud of dust and gas (a nebula) is pulled together by gravity. As the material falls inward, gravitational potential energy becomes thermal energy, so the core heats up. When the core is hot enough, hydrogen nuclei fuse to form helium, releasing energy. That energy raises the pressure and pushes outward, while gravity pulls inward. When the two balance, the star is in equilibrium and stays stable for a long time. The Sun formed this way. In the wider lifecycle, a star of the Sun's mass later expands into a red giant, sheds its outer layers and leaves a white dwarf; more massive stars may end as neutron stars or black holes. A strong answer earns marks for these points. States that the Sun formed from dust and gas drawn together by gravity. Explains that gravitational collapse heats the core until hydrogen fusion begins. Describes equilibrium as a balance between inward gravitational collapse and outward pressure from energy released in fusion. Identifies that the Sun is a main-sequence star and outlines later stages such as red giant and white dwarf. A common slip: Claims that fusion causes the cloud to collapse. Instead, stating that gravity causes the collapse and fusion releases the outward energy. Exam tip: Link each stage to the force or energy involved: gravity inward, fusion energy outward.
Key words
Say what each word means before you turn the card.
Formation of the Sun from dust and gas
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Gravity and core heating
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Fusion reactions releasing energy
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Equilibrium between collapse and expansion
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See every definition
- Formation of the Sun from dust and gas
- Our Sun was formed from dust and gas drawn together by gravity.
- Gravity and core heating
- As the material falls inward, gravitational potential energy becomes thermal energy, so the core heats up.
- Fusion reactions releasing energy
- When the core is hot enough, hydrogen nuclei fuse to form helium, releasing energy.
- Equilibrium between collapse and expansion
- Energy released in fusion raises the pressure and pushes outward while gravity pulls inward, and when the two balance the star is in equilibrium.
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