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.