Newton's Law of Universal Gravitation
Every two point masses attract with F = G m1 m2 / r2 along the line joining them.
What is Newton's Law of Universal Gravitation?
Every two point masses attract with F = G m1 m2 / r2 along the line joining them.
Key formula / rule: F = G m1 m2/r2 with G = 6.67 x 10-11 N m2 kg-2.
Key points
- Apply the inverse-square law to two-body and multi-body systems.
- Explain the shell result for uniform spheres.
Common exam trap
Measuring r from the surface rather than the centre.
Definitions
- Term
Newton's Law of Universal Gravitation
- Meaning
Every two point masses attract with F = G m1 m2 / r2 along the line joining them.
- Term
Newton's Law of Universal Gravitation — explanation
- Meaning
The law is universal and always attractive, and superposition applies for many bodies. For spherically symmetric bodies the distance is measured from the centre.
Learning objectives
Apply the inverse-square law to two-body and multi-body systems.
Explain the shell result for uniform spheres.
Formulae
- Key point
F = G m1 m2/r2 with G = 6.67 x 10-11 N m2 kg-2.
- Key point
Forces from several masses add vectorially.
- Key point
A uniform sphere acts as a point mass at its centre for external points.
Prerequisites
PHY-U1-NLM-T1-S1-C2
Common mistakes
Measuring r from the surface rather than the centre.
Assuming gravitational force can be shielded like an electric field.
Keywords
Newton
Universal
Gravitation
Practice preview
The universal gravitational constant G has a value of approximately 6.674 x 10^-11 N m^2 kg^-2. What does the term "universal" imply about this constant?…
easy
What is the mathematical expression for Newton's Law of Universal Gravitation between two point masses m1 and m2 separated by a distance r?…
easy
Two point masses m1 and m2 are separated by a distance d. If the distance between them is increased by 50%, by what percentage does the gravitational force between them decrease?…
hard