Newton's Law of Gravitation
Every two masses attract with a force F = Gm₁m₂/r².
About this topic
Every two masses attract each other with a force F = Gm₁m₂/r², where G = 6.67 × 10⁻¹¹ N·m²/kg² and r is the distance between their centres. The force grows with the masses and falls with the square of distance, an inverse-square law. Because G is so tiny, the force is only noticeable when at least one mass is huge, like a planet.
Newton showed that the same force that pulls an apple to the ground also holds the Moon in orbit, unifying earthly and heavenly motion for the first time. The forces on the two bodies are equal and opposite, as Newton's third law demands: Earth pulls you down exactly as hard as you pull Earth up, though Earth's enormous mass means its acceleration is negligible.
Worked example: doubling the distance between two masses cuts the force to one quarter, and tripling it cuts it to one ninth. Two 1 kg masses 1 m apart attract with only 6.67 × 10⁻¹¹ N, far too small to feel, which is why Cavendish needed a delicate torsion balance to measure G.
The law lets us weigh planets, predict orbits, plan spacecraft trajectories and discover unseen planets such as Neptune from the wobble of Uranus. Common misconceptions: gravity does not stop in space, and heavier objects do not fall faster in the absence of air, because the larger force is balanced by the larger mass.
Key ideas
- Force falls with the square of distance
- G = 6.67 × 10⁻¹¹ N·m²/kg²
- Gravity is always attractive
Quick check
Use cases: where Newton's Law of Gravitation helps
- Homework: review the key idea behind Newton's Law of Gravitation before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Newton's Law of Gravitation without notes.
- Visual learning: play with the interactive lab to see how Newton's Law of Gravitation changes when you adjust its inputs.
- Teaching a friend: explain Newton's Law of Gravitation in your own words, then compare your version with the key ideas.
The same laws describe car crashes, sports, satellites and everyday machines.
Frequently asked questions
What is Newton's Law of Gravitation?
Every two masses attract with a force F = Gm₁m₂/r².
What will I learn in Newton's Law of Gravitation?
Force falls with the square of distance. G = 6.67 × 10⁻¹¹ N·m²/kg². Gravity is always attractive.
Is Newton's Law of Gravitation part of Physics?
Yes. It is one of 150 Physics topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Newton's Law of Gravitation lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Newton's Law of Gravitation?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
No account is needed. Marking a topic as learned is saved in your own browser, so it stays on that device and is not sent to a server.