Cambridge IGCSE Physics Notes 1.6: Momentum
Cambridge IGCSE Physics momentum notes on momentum, impulse, force-time relationships, conservation, collisions, and safety applications.
Q: What does Cambridge IGCSE Physics Notes 1.6: Momentum cover?
A: It follows official Cambridge Physics section 1.6 for syllabuses 0625 and 0972, with Core ideas separated from Supplement depth.
Momentum combines mass and velocity. In an isolated system total momentum is conserved, while force changes momentum over time.
The ideas that organise this section
- Momentum is a vector, so direction signs matter.
- Conservation applies to the total system when external resultant force is negligible.
- Increasing collision time reduces average force for the same momentum change.
Core route
Core candidates should be ready to describe, calculate, interpret, and apply the following:
- Calculate momentum and describe safety features that increase stopping time.
- Relate force to a change in momentum qualitatively.
- Apply conservation to straightforward one-dimensional interactions.
Supplement route
Extended candidates study all Core content and add the following depth:
- Use impulse and force-time relationships quantitatively.
- Solve collision and recoil problems with a consistent positive direction.
- Connect the area under a force-time graph to impulse when presented with data.
Formula route
- Relationship: momentum = mass x velocity.
- Relationship: impulse = force x time = change in momentum.
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 Momentum, 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
An airbag reduces injury risk by increasing the time over which the passenger's momentum falls to zero, reducing average force.
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
- Ignoring direction in a collision.
- Conserving kinetic energy in every collision.
- Applying momentum conservation to one object instead of the chosen system.
Assessment guidance
Questions on Momentum 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 Momentum. 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
Use the mechanics practical post for trolley timing, velocity measurement, repeated trials, and collision-data limitations.
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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