Concepts

Terminal velocity and the velocity dependence of the drag force

Overview

Coffee filters are dropped singly and nested together, and from various heights. The velocity and acceleration of the filters are measured.

Details

Equipment

• Coffee filters
• [1] Stopwatch
• [1] Lab stand
• [1] 90-degree clamp
• [1] Rod
• [1] String
• (Optional) [1] Metre stick
• (Optional) [1] Venier motion sensor

Important Notes

• The filters, especially the single filter, have a tendency to flutter. A string was hung from the ceiling above the motion sensor to provide a guide for dropping the filters. 

Script

1. Drop a single coffee filter. Note its motion.
2. Drop two filters nested together. Compare their motion to the single coffee filter.
3. Drop the single filter from a height of 1 metre. Ask the students to guess from what height the nested filters should be dropped for them to reach the ground at the same time as the single filter dropped at 1 metre. It turns out that this height is very close to 1.4 metres, suggesting that the drag force in this case goes as the velocity squared.
4. (Optional) Measure the velocity of the filters using the Vernier software motion sensor and MacMotion.

Additional Resources