Universal Law of Gravitation

Explore how Newton discovered that every object in the universe attracts every other object, from falling apples to orbiting moons.

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"If Earth attracts the apple, does it also attract the Moon?"
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Tangential Velocity
Gravitational Force
(Centripetal)
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Object A
Mass (kg)
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Object B
Mass (kg)
F = G × (M × m) / d²
F = 6.67×10⁻¹¹ × (100 × 50) / 10²
F = 3.34 × 10⁻⁸ N
Explore Gravitation
Activity 9.1: Stone and Thread Experiment
Universal Law of Gravitation
Every object in the universe attracts every other object with a force which is proportional to the product of their masses and inversely proportional to the square of the distance between them. The force is along the line joining the centres of two objects.
F = G × (M × m) / d²
Where:
F = Gravitational force (N)
G = 6.67 × 10⁻¹¹ N m² kg⁻² (Universal gravitational constant)
M, m = Masses of the two objects (kg)
d = Distance between centers (m)
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Newton's Insight
Newton realized that the same force that makes an apple fall also keeps the Moon in orbit around Earth. This was a revolutionary unification of terrestrial and celestial mechanics.
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Centripetal Force
Objects in circular motion require a center-seeking force. For celestial bodies, gravity provides this centripetal force, preventing them from flying off in straight lines.
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Action-Reaction
By Newton's third law, if Earth attracts an apple, the apple attracts Earth equally. We don't see Earth move because its mass is enormously larger than the apple's.
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Universal Application
The law applies to all objects: from tiny particles to massive stars. It explains planetary orbits, tides, and why we stay grounded on Earth's surface.
Importance of Gravitational Law
The universal law of gravitation explains:
• The force that binds us to Earth
• The motion of the Moon around Earth
• The motion of planets around the Sun
• Ocean tides caused by the Moon and Sun