1. Grid A plastic grid covers the open end of a cylindrical vessel containing water. The grid is covered and the vessel is turned upside down. What is the maximal size of holes in the grid so that water does not flow out when the cover is removed?

2. Overview • Theory1 – why water flows out • Experiment1 – picture and movie • Theory2 – bigger holes make water flow out easier • Theory3 – the more holes it has, the easier water will flow out.

3. Overview • Experiment2 – hole’s number • Theory4 – different conditions will have different maximum hole size. • Experiment3 – the maximum size • Conclusion

4. Theory1 • Theoretically, air pressure is stronger than water pressure, so the water should not flow out.

5. Theory1 • But the tube can’t be perfectly horizontal • The natural tilt and oscillation will make the water surface act like this:

6. h h Theory1 • There will be a pressure caused by • The pressure will destroy the original balance.

7. Theory1 • So the water surface will collapse. • Air will get in and water will flow out

8. Experiment1

9. Experiment1

10. h1 h2 h2 h1 Theory2 • Bigger holes make water flow out easier. • > => P2 > P1

11. h2 h1 h1 h2 Theory3 • The more holes it has, the easier water will flow out • > => P2 > P1

12. Experiment2 – hole’s number • Condition: – Tube length: 25cm – Tube diameter: 4.9cm – Space between holes:5mm – Hole size: 10*10 (mm) • Parameter: – 1, 2, 3, 4 (holes)

13. 1 hole 2 holes 3 holes 4 holes success fail success fail fail fail

14. Experiment2 – hole’s number

15. Theory4 • Different condition will have different maximum hole size.

16. Experiment3 – maximum size • Condition: – Tube length: 25cm – Tube diameter: 4.9cm – Space between holes:5mm – 4 holes • Parameter: 4 sizes of holes: 5*5, 6*6, 7*7, 8*8 (mm)

17. 5*5 mm 6*6 mm

18. 7*7 mm 8*8 mm

19. Experiment3 – maximum size

20. Experiment3 – maximum size • In this condition, the maximum size of holes is an 8*8 square.

21. Conclusion • Water flows out because of natural tilt. • Bigger holes make flowing easier. • More holes make flowing easier. • Different condition, different size.