Free fall and terminal velocity
This is Cambridge International IGCSE Physics 0625, separate from the Egyptian Baccalaureate / Thanaweya Amma and not a Year 3 course. First learn the Core idea that g is approximately constant near Earth. Then explore the clearly labelled Supplement / Extended material about air and liquid resistance.
What is free fall?
In the ideal physics model, an object is in free fall when gravity is the only force acting on it. We ignore air resistance. Near Earth’s surface, the acceleration of free fall is approximately constant. We write it as g.
Open the worked example
Imagine dropping a small ball a few metres above the ground. Over this short fall, we can treat g as about 9.8 m/s² and almost unchanged. The ball’s acceleration points downwards, towards Earth.
Quick check: In the ideal free-fall model, which force acts on the falling object?
Think, then reveal: Gravity alone. Real air can exert resistance, but ideal free fall ignores it.
See how speed and forces change during a fall
Interactive model · follow the fall
Choose a situation, then move the slider along time. The graphs are qualitative sketches, not experimental measurements.
Motion: Speed is still rising, but growing resistance makes the acceleration smaller.
Forces: Resistance is growing; the downward resultant force is getting smaller.
Supplement / Extended · explore g × time
Assume an object starts from rest, falls freely and air resistance is ignored. Change the time to see the ideal speed increase.
speed increase = g × t = 9.8 m/s² × 2.0 s = 19.6 m/s
The units reduce to m/s. This is a model for free fall, not a prediction for a skydiver in air.
Practise, then read the explanation
Questions marked Supplement / Extended use the extra resistance and terminal-velocity ideas. Try first, open the optional hint if helpful, then submit to see the reasoning.
Optional hint
Think about which force acts in the ideal free-fall model.
Original lesson and practice align to Cambridge IGCSE Physics 0625 syllabus objectives 1.2.8 (Core: approximately constant acceleration of free fall near Earth) and 1.2.13 (Supplement / Extended: falling with and without resistance). Source reading: Physics-0625 Volume A, PDF pp. 33–35 (printed pp. 25–27). Resistance graphs are labelled qualitative sketches; the source does not supply measured data.