Newton’s Law of Gravitation — A/L Physics

What must I remember about Newton’s Law of Gravitation?

• Newton's Universal Law of Gravitation: Every point mass attracts every other point mass with a force directly proportional to the product of their masses and inversely proportional to the square of the distance between them: F = G (m1 m2) / r².
• Universal Gravitational Constant (G): Fundamental physical constant G ≈ 6.674 × 10⁻¹¹ N·m²·kg⁻² = kg⁻¹·m³·s⁻²; dimension [M⁻¹ L³ T⁻²].
• Spherical Shell Theorem (Newton): A uniform spherical shell of mass M attracts an external particle as if all its mass were concentrated at its geometric center; inside the shell, gravitational force is identically ZERO everywhere.
• Acceleration Due to Gravity (g) at Earth's Surface: g0 = (G M_E) / R_E² ≈ 9.81 m/s²; links microscopic laboratory measurements of G to planetary mass.

Test yourself (1 minute)

1. Independent of intervening medium

   Gravitational force between two masses is completely unaffected by the presence of any intervening physical medium or shielding.

2. Earth's mass determination

   Mass of Earth M_E = (g0 R_E²) / G ≈ 5.97 × 10²⁴ kg (the 'weighing of the Earth').

Practise Newton’s Law of Gravitation questions today

Must know

• Gravitational force is strictly attractive, central (acts along the line joining centers of masses), conservative, and obeys inverse square law.

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 5: Gravitational Fields

What comes next?

Next in the syllabus

Where does Newton’s Law of Gravitation fit in the syllabus?

Unit 5.1 · Year 1 · Term 3