Gravitation: Key Terms (Form 4 SPM Physics)

Terms and definitions

• Newton's universal law of gravitation, Every mass attracts every other mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centres.
• Gravitational field, A region around a mass in which another mass experiences a gravitational force of attraction.
• Gravitational field strength, The gravitational force acting on each kilogram of mass at a point in a field; measured in newtons per kilogram (N kg⁻¹).
• Kepler's laws, Three laws describing planetary motion: orbits are ellipses, a line to the planet sweeps equal areas in equal times, and the square of the orbital period is proportional to the cube of the orbital radius.
• Satellite, An object that orbits a larger body, such as the Moon around the Earth or a man-made satellite kept in orbit by gravitational force.
• Geostationary orbit, An orbit above the equator in which a satellite has a period of 24 hours, so it appears to stay above the same point on the Earth's surface.
• Escape velocity, The minimum velocity an object needs to completely escape the gravitational pull of a planet or other body.
• Orbital velocity, The velocity a satellite must have to stay in a stable orbit at a given radius, where gravitational force provides the centripetal force.
• Universal gravitational constant, The universal constant G in Newton's law of gravitation, with a value of about 6.67 × 10⁻¹¹ N m² kg⁻².
• Centripetal force, The net force directed towards the centre of a circle that keeps an object moving in a circular path, such as a satellite in orbit.
• Base quantity, A physical quantity that cannot be defined in terms of other physical quantities; the five in physics are length, mass, time, electric current and temperature. (related term from another chapter)
• Derived quantity, A physical quantity obtained by combining base quantities through multiplication or division, such as speed or density. (related term from another chapter)
• Scalar quantity, A physical quantity that has magnitude only, with no direction, such as distance, speed and mass. (related term from another chapter)
• Vector quantity, A physical quantity that has both magnitude and direction, such as displacement, velocity and force. (related term from another chapter)
• SI unit, The internationally agreed system of units for physical quantities, based on the seven SI base units such as the metre, kilogram and second. (related term from another chapter)

Content standards these terms come from

• 3.1 Newton's Universal Law of Gravitation
• 3.2 Kepler's Laws
• 3.3 Man-made Satellites

How to learn them

1. Cover the definition, say it aloud, then check the unit.
2. Pair each term with a formula or experiment from the chapter.
3. Write the Malay term alongside the English one, SPM papers are bilingual.

More Gravitation resources

• Chapter overview: Gravitation
• Revision Notes
• Common Mistakes
• Practice Questions
• Paper 2 Answering Guide
• Paper 3 Guide
• Calculation practice sets

Source: DSKP KSSM Physics Form 4 and 5 (Versi English), Sijil Pelajaran Malaysia: Format Pentaksiran mulai 2021, Fizik (4531) (Bahagian Pembangunan Kurikulum (BPK), KPM)