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?

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.

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

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

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

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

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

Experiment1

Experiment1

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

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

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)

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

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

Theory4 Different condition will have different maximum hole size.

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)

5*5 mm 6*6 mm

7*7 mm 8*8 mm

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

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

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