Cambridge IGCSE Physics Notes 6.1: Earth and the Solar System
Cambridge IGCSE Physics space notes on Earth, Moon, day, year, seasons, gravity, orbits, planets, minor planets, comets, and orbital speed.
Q: What does Cambridge IGCSE Physics Notes 6.1: Earth and the Solar System cover?
A: It follows official Cambridge Physics section 6.1 for syllabuses 0625 and 0972, with Core ideas separated from Supplement depth.
Solar-System motion is governed by gravity, with rotation explaining day, orbit explaining year, and axial tilt explaining seasons.
The ideas that organise this section
- Separate rotation on an axis from revolution in an orbit.
- Seasons result from axial tilt and changing sunlight angle, not large changes in Earth-Sun distance.
- Gravity supplies the inward force required for orbital motion.
Core route
Core candidates should be ready to describe, calculate, interpret, and apply the following:
- Describe Earth, Moon, and Solar-System structure and motions.
- Explain day, year, Moon phases, and seasons at the required qualitative level.
- Describe planets, minor planets, comets, and satellites.
Supplement route
Extended candidates study all Core content and add the following depth:
- Use orbital speed, radius, and period relationships.
- Explain changing comet speed qualitatively through gravitational energy changes.
- Relate gravitational field strength and orbital behaviour to mass and distance.
Formula route
- Relationship: orbital speed = 2 x pi x orbital radius / period.
Write the relationship before substituting. Convert units first, keep extra figures during working, and round only the final answer to sensible precision.
Build a connected model
In Earth and the Solar System, a strong answer connects the named quantity or model to observable evidence. Begin by defining the physical quantity in words or with its relationship. Identify which values are scalars and which require a direction. Represent the situation with a labelled diagram, graph, field pattern, ray or circuit when that makes the relationship visible. The representation is part of the reasoning: its labels, arrows and scale should agree with the written explanation.
For a calculation, write the governing relationship before substitution, convert prefixes and time units, keep unrounded values during working and attach the correct final unit. For a qualitative question, use a cause-link-consequence chain. Name what changes, state the physical mechanism that links the change to the system, and then give the measurable result. If two cases are compared, hold unrelated variables constant and use the same physical principle for both.
Check the answer against limiting cases. A zero input, a doubled input or a reversed direction often exposes an incorrect proportionality or sign. Also check whether the value is plausible for the apparatus or context. This final check is especially important when a calculator gives a precise-looking result from an incorrect unit conversion.
Worked reasoning example
A planet in a smaller orbit generally travels faster because the Sun's gravitational field is stronger closer to the Sun.
For explanation questions, state the physical principle, apply it to the named system, then give the consequence. A formula or keyword by itself is not a complete explanation.
Extend the example by identifying the evidence that would distinguish the correct model from a tempting alternative. State what would be measured or observed, which variable must remain controlled, and how the conclusion follows from the result. This turns a numerical or descriptive answer into a testable physical argument. When the question asks for an explanation rather than a calculation, preserve the same chain but express it as principle, application and consequence.
A reliable answer method
- Identify the quantity, law, graph feature, or physical model being tested.
- Mark a positive direction or label the diagram when direction matters.
- Write the equation or principle before inserting data.
- Keep units consistent and show the main substitution.
- Check whether the magnitude, direction, trend, and unit are physically reasonable.
Common mistakes
- Explaining seasons by Earth being closer to the Sun in summer.
- Confusing Moon phases with eclipses.
- Drawing an orbit without an inward gravitational force.
Assessment guidance
Questions on Earth and the Solar System can mix recall, calculation, graph or diagram interpretation and unfamiliar application. Read the command word first. A definition needs the precise physical meaning; a description reports a pattern; an explanation supplies the mechanism; and an evaluation weighs evidence or method quality. Show equations and substitutions so method marks remain visible. Label every diagram and state directions where relevant. In multi-step problems, carry forward unrounded values and make the final answer's unit and significant figures consistent with the data. Never rely on a memorised keyword when the question asks how or why a result occurs.
Retrieval practice
Without notes, rebuild the Core and Supplement lists for Earth and the Solar System. Define every named quantity, reproduce the principal relationship or representation and explain one everyday application. Then solve one direct calculation and one unfamiliar context, checking units and limiting cases. Finish by writing two misconception corrections and one practical measurement that could test the topic's main relationship.
Theory and practical stay separate
Space physics is mainly model and data work; use the practical hub's planning and graph notes for scale models, orbital data, and evaluation.
Official source
Cambridge International, Physics 0625 syllabus for examinations in 2026, 2027 and 2028. Cambridge states that Physics 0972 is graded from 9 to 1 but otherwise follows the same subject content as 0625.
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