A skydiver does not get faster and faster forever. The air pushes back harder the quicker they fall, until that push exactly matches their weight. From that moment the speed holds perfectly steady, and they have reached terminal velocity.
An object falling through a fluid has a constant weight downward and a drag (resistance) upward that grows with speed. When drag grows to equal the weight, the resultant force is zero, so there is no acceleration and the object falls at a constant terminal velocity.
Section 01
Drag catches up with weight.
Release the skydiver and watch the two arrows. Weight stays the same. Drag starts at zero and grows as they speed up. Once terminal velocity is reached, the deploy-parachute control unlocks: use it to change the surface area and watch the forces flip.
Stage 1 · Learn
Check the force balance
Four quick checks on drag, weight, and terminal velocity. Each correct answer earns XP and lights this skill on your star map.
Quick check+10 XP
As a falling object speeds up, the drag (air resistance) acting on it...
Quick check+10 XP
At terminal velocity, the drag force is...
Quick check+10 XP
At terminal velocity, the resultant force on the object is...
Quick check+10 XP
Opening a parachute increases the surface area, which...
Section 02
Three stages of a fall.
Just released: drag is very small, so weight is much larger; the resultant force is large and downward, and the object accelerates at close to g.
Speeding up: as the speed rises, drag rises too, so the resultant force shrinks and the acceleration slowly falls; the velocity-time curve bends over.
Terminal velocity: drag has grown to equal the weight, the resultant force is zero, the acceleration is zero, and the object falls at a constant velocity.
Examiner trap
At terminal velocity the object is still moving, and moving fast, yet the resultant force is zero. Drag equals weight, so they cancel. A common mistake is to think a moving object must have a forward or downward resultant force. It does not: constant velocity and balanced forces go together, the same idea as a car cruising at a steady speed.
Worked example
A skydiver opens their parachute. Describe and explain the immediate effect on their velocity and the forces acting on them.
Step 1 · Immediate force balanceOpening the parachute greatly increases the surface area, which immediately causes a large increase in air resistance (drag). The drag is now much larger than the weight.
Step 2 · The resultant forceBecause drag acts upward and is larger than the downward weight, the resultant force is now upward.
Step 3 · Effect on motionAn upward resultant force on a falling object makes it decelerate. The skydiver slows until drag shrinks back to equal the weight again, reaching a new, much safer terminal velocity.
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written in the style of Paper 2.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
Just after release, before much speed has built up, the acceleration of a skydiver is...
Exam style+20 XP
A skydiver falling at a steady terminal velocity has a resultant force that is...
Exam style+20 XP
Immediately after a parachute opens, the skydiver...
Skill unlocked
Terminal velocity, mastered.
This skill is now lit gold on your star map. That completes the motion topic.
Mixed questions across the whole unit, each one worth XP. Start this only when you feel confident across every topic in the unit, not just terminal velocity.