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

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

8. Experiment1

9. Experiment1

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

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

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

14. Experiment2 – hole’s number
Success or fail
Condition
1 hole
Success
Will fail at
20~30 degrees
2 holes
10~15 degrees
3 holes
Fail
4 holes

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
Size (mm)
Success or fail
Condition
5*5
Success
Succeed easily
6*6
7*7
8*8
Succeed only below 3~5 degrees

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.