Terminal velocity experiment (PAG 1.2)

Estimating Terminal Velocity

The video demonstrates how to estimate the terminal velocity of a ball bearing falling through a viscous liquid, such as thick oil.

Equipment

• A clear tube filled with viscous fluid
• A ball bearing
• A stopwatch or video timer
• A chinagraph pencil or rubber bands to mark positions on the tube
• A magnet to retrieve the ball bearing

Method

1. Drop the ball bearing into the liquid and start timing as it enters the fluid.
2. Mark the ball’s position on the tube at one-second intervals. Use a pencil or place rubber bands around the tube.
3. Retrieve the ball with the magnet so you can inspect its motion and the marks.
4. Measure the distance between successive marks. Since each interval represents one second, divide each distance by one second to find the ball’s average velocity over that interval.
5. Compare the velocities from one interval to the next. When the ball covers roughly equal distances in equal time intervals, its speed is approximately constant, indicating that it has reached terminal velocity.

Recording the experiment on video and using the video timer can improve the timing.

Speaker and Source

• Narrator: Cowen Physics presenter; the speaker is not named in the subtitles.
• Source: Cowen Physics.