Study Notes
The gravitational field of a point mass describes how the gravitational field strength (g) varies with distance from a mass. It is derived using Newton's law of gravitation and is crucial for understanding gravitational interactions.
- Gravitational Field Strength (g) — the force per unit mass at a point in a gravitational field. Example: g = GM/r^2, where G is the gravitational constant, M is the mass, and r is the distance from the mass.
- Newton's Law of Gravitation — describes the force between two masses. Example: FG = GMm/r^2, where FG is the gravitational force, M and m are the masses, and r is the distance between them.
- Inverse Square Law — describes how gravitational field strength decreases with distance. Example: g ∝ 1/r^2, meaning g decreases as the square of the distance increases.
Exam Tips
Key Definitions to Remember
- Gravitational Field Strength (g) is the force per unit mass at a point.
- Newton's Law of Gravitation describes the force between two masses.
Common Confusions
- Confusing gravitational field strength with gravitational force.
- Misunderstanding the inverse square law relationship.
Typical Exam Questions
- How do you calculate gravitational field strength (g) at a point? Use g = GM/r^2, substituting the values for G, M, and r.
- What happens to g as you move away from the Earth's surface? It decreases following the inverse square law.
- Why is g approximately constant on Earth's surface? Because the Earth's radius is much larger than small height variations.
What Examiners Usually Test
- Understanding of how to derive and calculate g.
- Application of the inverse square law in different scenarios.