Gravitational Field

Definition

The region around a massive object (such as Earth, Sun, etc.) where gravitational force is operative is termed as a gravitational field.

Gravitational Field Strength

The amount of force per unit mass acting on objects in the gravitational field.

g = F / m

Where: g = Gravitational field strength, F = Force, m = Mass

  • Measured in newtons per kilogram (N/kg)
  • Vector quantity pointing toward the center of Earth
  • On Earth's surface: g = 9.8 N/kg or g = 9.8 m/s²

Gravitational Field Strength in the Solar System

Planetg (N/kg)
Mercury3.7
Venus8.9
Earth9.8
Mars3.7
Jupiter24.7
Saturn9
Uranus8.7
Neptune11
Sun274

Example: Gravitational Field Strength on an Unknown Planet

Given:

  • Weight on Earth: W = 400 N
  • Weight on unknown planet: W = 150 N
  • Gravitational field strength on Earth: g = 9.8 N/kg

Solution:

W₁ / g₁ = W₂ / g₂

150 N / g = 400 N / 9.8 N/kg

g = (150 N * 9.8 N/kg) / 400 N = 3.675 N/kg

The unknown planet is Mars (the red planet), the nearest planet to Earth.