Lesson 07
Review
Review the gravitational fields test and strengthen weak areas.
Objectives
Lesson outcomes
- Correct errors from the B1 gravitational fields test using clear physics reasoning.
- Identify whether mistakes came from definitions, model choice, radius, signs, units, or orbital conditions.
- Set targeted follow-up practice for the weakest part of gravitational fields.
Syllabus
CIE 9702 syllabus points
12 linked
- 13.1.1 understand that a gravitational field is an example of a field of force and define gravitational field as force per unit mass
- 13.1.2 represent a gravitational field by means of field lines
- 13.2.1 understand that, for a point outside a uniform sphere, the mass of the sphere may be considered to be a point mass at its centre
- 13.2.2 recall and use Newton’s law of gravitation F = Gm1m2 / r2 for the force between two point masses
- 13.2.3 analyse circular orbits in gravitational fields by relating the gravitational force to the centripetal acceleration it causes
- 13.2.4 understand that a satellite in a geostationary orbit remains at the same point above the Earth’s surface, with an orbital period of 24 hours, orbiting from west to east, directly above the Equator
- 13.3.1 derive, from Newton’s law of gravitation and the definition of gravitational field, the equation g = GM / r 2 for the gravitational field strength due to a point mass
- 13.3.2 recall and use g = GM / r 2
- 13.3.3 understand why g is approximately constant for small changes in height near the Earth’s surface
- 13.4.1 define gravitational potential at a point as the work done per unit mass in bringing a small test mass from infinity to the point
- 13.4.2 use ϕ = –GM / r for the gravitational potential in the field due to a point mass
- 13.4.3 understand how the concept of gravitational potential leads to the gravitational potential energy of two point masses and use EP = –GMm / r
Definitions
Required definitions
Gravitational field
a region where a mass experiences a force; gravitational field strength is force per unit mass.
Gravitational potential
the work done per unit mass in bringing a small test mass from infinity to the point.
Lesson Notes
Student guidance and lesson notes
Overview
This lesson uses the B1 gravitational fields test to improve your next round of revision. The aim is to understand why errors happened, correct them properly, and decide what needs more practice.
What You Need to Know
- A useful correction explains the physical model, not just the final answer.
- Common weak points include centre-to-centre distances, inverse-square reasoning, orbital radius, and potential signs.
- Field, force, orbit, and potential questions can look similar but use different starting models.
- Feedback should lead to a specific practice target.
How to Work Through It
- Sort your test errors by topic and skill: definitions, equations, diagrams, radius, units, or signs.
- Rewrite selected answers with the missing physics included.
- Rework at least one similar question without looking at the original solution.
- Finish with a short target for future gravitational fields revision.
Check Your Understanding
- Which mistake cost the most marks, and why?
- Was the weak step physics understanding, equation choice, radius, algebra, units, or exam wording?
- Can you now explain the corrected answer without reading from the mark scheme?
Common Mistakes
- Copying the mark scheme without identifying the original misconception.
- Correcting calculations while leaving the wrong model choice unchanged.
- Treating one weak orbit question as isolated when it shows a broader radius or period issue.
- Ignoring sign errors in potential questions because the magnitude looked plausible.
Next Steps
- Add the weakest B1 gravitational fields subtopic to your next independent revision cycle.
- Keep corrected examples available for later synoptic revision.