Describe the motion of objects falling in a uniform gravitational field with and without air/liquid resistance, including reference to terminal velocity

1.2 Motion – Falling Objects

Learning Objective (AO1)

Describe the motion of objects falling in a uniform gravitational field both without and with air or liquid resistance, and refer to the concept of terminal velocity.

Key Concepts

  • Uniform gravitational field: Near the Earth’s surface the acceleration due to gravity is essentially constant, g ≈ 9.81 m s⁻².

  • Free fall: Motion under gravity alone (no resistance).

  • Resisted fall: Motion under gravity together with a resistive (drag) force that opposes the motion.

  • Terminal velocity (vₜ): The constant speed reached when the upward drag force exactly balances the weight, giving zero net force and zero acceleration.

Free Fall – No Resistance

When air or liquid resistance is negligible the only force acting is the weight W = mg. The object therefore experiences a constant downward acceleration equal to g.

Key equation (AO1)

v = gt