| Difficulty | Secondary School | High school/other |
| ★ | Basic | Easy |
| ★★ | Demanding | Basic |
| ★★★ | Demanding | |
| ★★★★ | Difficult | |
| ★★★★★ | Very difficult |
Determine velocity of the bubble.
Tip: Measure the time spent by the bubble at certain distances and move the values to the (t, s) coordinate system. Fit a straight line to the points. What can you expect from the slope of the line?
Answer: $0{,}07\ m/s$