Key Concepts: Gravitational Field Strength

Gravitational Field

• A gravitational field exists around every mass. Any other mass placed in the field experiences a force.
• Gravitational field strength (g): Force per unit mass at a point in the field.
• g = F/m = GM/r² — units: N/kg or m/s².

Field Lines

• Field lines point toward the mass (gravity is attractive).
• Closer lines = stronger field. Lines are radial around a point mass.
• Near Earth's surface, field lines are approximately parallel (uniform field).

Gravitational Potential Energy

• Near surface: PE = mgh.
• General: PE = −GMm/r (negative because work must be done against gravity to move mass to infinity).
• PE = 0 at infinite separation (by convention).