Gravitational Fields

Gravity is the force of attraction between any two objects with mass. Although it is the weakest of the four fundamental forces, it dominates on the largest scales because it acts over infinite range and is always attractive. Unlike the electric force, gravity cannot be shielded or repulsive. This topic is tested in AQA Paper 2 (Section 7) and OCR Paper 1 (Module 5), and draws many parallels with electric fields — examiners frequently test your ability to compare the two.

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Newton's Law of Universal Gravitation

Key Definition: Newton's Law of Universal Gravitation states that every particle in the universe attracts every other particle 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.

F = −GMm/r²

where G is the gravitational constant (6.67 × 10⁻¹¹ N m² kg⁻²), M and m are the two masses, and r is the distance between their centres. The negative sign indicates the force is always attractive (directed towards the other mass).