Lesson 06
Test
Assess understanding 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 test checks the full B1 gravitational fields topic: field strength, Newton’s law of gravitation, point-mass fields, circular and geostationary orbits, gravitational potential, and potential energy.
What You Need to Know
- Show working clearly when using inverse-square relationships, circular motion, or potential equations.
- Use centre-to-centre distances for gravitational force, field strength, and orbital radius.
- Keep units consistent, especially when converting orbital periods or distances.
- Explain physical meanings, not just equation substitutions.
How to Work Through It
- Read each question carefully and identify whether it is a force, field, orbit, or potential model.
- Write down known quantities, convert units, and define r from the correct centre.
- Keep vector direction, circular motion, and negative potential values clear in your working.
- Check final answers for units, significant figures, and physical sense.
Check Your Understanding
- Can you define gravitational field strength and represent a field with field lines?
- Can you use Newton’s law of gravitation and derive or use g = GM / r^2?
- Can you analyse a circular orbit by linking gravity to centripetal acceleration?
- Can you use gravitational potential and potential energy with the correct sign?
Common Mistakes
- Choosing an equation from keywords without checking the model.
- Using altitude instead of radius from the centre of Earth.
- Dropping negative signs in potential questions.
- Giving incomplete geostationary orbit conditions.
Next Steps
- Use the review lesson to correct mistakes and identify which B1 skills need more practice.
- Keep working visible so feedback can target the exact weak step.