AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
Eventually the resultant force will be zero and the object will move at…
Full specification wording
Acceleration: Eventually the resultant force will be zero and the object will move at its terminal velocity.
As the falling object speeds up, the drag from the fluid keeps increasing until it equals the weight in size.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 22 of 23
Study notes
From the checked teaching notes for this specification point.
The idea
As the falling object speeds up, the drag from the fluid keeps increasing until it equals the weight in size. The two forces are then balanced, there is no resultant, and the object stops accelerating and carries on at a steady velocity, its terminal velocity. Note that it does not slow down; it simply stops speeding up. A heavier object of the same shape needs a larger drag to balance its greater weight, so it must reach a higher speed first and its terminal velocity is greater, which is why a large hailstone lands faster than a small one. Opening a parachute increases the drag sharply, so the resultant force acts upwards, the skydiver slows, and a new and much lower terminal velocity is reached.
What earns the marks
- The drag or air resistance increasing as the velocity increases.
- The drag becoming equal to the weight.
- The resultant force then being zero.
- The object moving at a constant velocity, the terminal velocity.
Common mistakes and how to put them right
Saying the object slows down when it reaches terminal velocity.
Claiming the weight decreases until it matches the air resistance.
Stating that a zero resultant force means the object stops.
Leaving out the increase in drag with speed, which is the step that makes the balance happen.
Exam tips
- Three sentences, three marks: drag increases, drag equals weight, resultant is zero.
- Constant velocity and zero resultant force always go together, so quote whichever the question has not given you.
Try the lesson
The start of the Acceleration: Eventually the resultant force will be zero and the object will move at its terminal velocity. lesson, made from checked teaching notes for this specification point.
Have a go first
A skydiver jumps from a plane and falls. At first the skydiver accelerates, but later the resultant force on the skydiver becomes zero. What happens to the skydiver's velocity at the moment the resultant force becomes zero?
Listen
As the falling object speeds up, the drag from the fluid keeps increasing until it equals the weight in size. The two forces are then balanced, there is no resultant, and the object stops accelerating and carries on at a steady velocity, its terminal velocity. Note that it does not slow down; it simply stops speeding up. A heavier object of the same shape needs a larger drag to balance its greater weight, so it must reach a higher speed first and its terminal velocity is greater, which is why a large hailstone lands faster than a small one. Opening a parachute increases the drag sharply, so the resultant force acts upwards, the skydiver slows, and a new and much lower terminal velocity is reached. A strong answer earns marks for these points. the drag or air resistance increasing as the velocity increases. the drag becoming equal to the weight. the resultant force then being zero. the object moving at a constant velocity, the terminal velocity. Exam tip: Three sentences, three marks: drag increases, drag equals weight, resultant is zero.
See it
Put it in order
Put these steps in the order they happen.
- 1. Drag from the fluid increases
- 2. Drag equals weight in size
- 3. Object falls and speeds up
- 4. Object stops accelerating and moves at constant velocity, its terminal velocity
- 5. Resultant force is zero
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of Acceleration: Eventually the resultant force will be zero and the object will move at its terminal velocity.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge