What is meant by terminal velocity?

Terminal velocity is the constant velocity reached when the resistive force on a moving object has grown until it balances the driving force, leaving no resultant force.

Describe how the acceleration of an object falling through air changes from release until terminal velocity is reached.

It starts at g and falls steadily as the drag increases with speed, reaching zero when the drag has grown equal to the weight.

Describe the shape of the velocity–time graph for an object falling to terminal velocity.

It starts with a steep gradient which decreases steadily, and the curve levels off at the terminal velocity.

OCR A-Level Physics B H557

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Space, Time and Motion

Terminal velocity and resistive forces

3 things to know
Components 01, 02 and 03

Overview

Recall questions on how acceleration changes during a fall, the velocity–time graph, forces on a ball bearing in a viscous liquid, marker placement, nested paper cones, and falling in a vacuum.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How can terminal velocity be investigated using a ball bearing in a viscous liquid?

Key term

In the falling ball-bearing experiment, how do you know that terminal velocity has been reached?

Key term

Why should the first marker be placed some way below the surface of the liquid in the ball-bearing experiment?

Questions from this subtopic

Each one with the model answer underneath.

1
What is meant by terminal velocity?
Model answer
Terminal velocity is the constant velocity reached when the resistive force on a moving object has grown until it balances the driving force, leaving no resultant force.
2
Describe how the acceleration of an object falling through air changes from release until terminal velocity is reached.
Model answer
It starts at g and falls steadily as the drag increases with speed, reaching zero when the drag has grown equal to the weight.
3
Describe the shape of the velocity–time graph for an object falling to terminal velocity.
Model answer
It starts with a steep gradient which decreases steadily, and the curve levels off at the terminal velocity.
4
How can terminal velocity be investigated using a ball bearing in a viscous liquid?
Model answer
A ball bearing is dropped into a tall tube of glycerol marked with rubber bands at equal intervals, and the time to fall between successive marks is measured with a stopwatch or light gates.
5
In the falling ball-bearing experiment, how do you know that terminal velocity has been reached?
Model answer
The times taken to fall between successive equally spaced marks become equal to one another.
6
Why should the first marker be placed some way below the surface of the liquid in the ball-bearing experiment?
Model answer
The ball needs a short distance to reach terminal velocity, and timing should only begin once its velocity has become constant.

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