1. Topic 11

2. Outline 1.Official description 2.Hypothesis 3.Preparation for experiment 4.Experiment 1~3 5.Result 6.Explanation 7.Conclusion

3. Official Description Dry sand is rather ‘soft' to walk on when compared to damp sand. However,sand containing a significant amount of water becomes soft again. Investigate the parameters that affect the softness of sand.

4. Hypothesis STAGE3 Wet & soft STAGE3 Wet & soft STAGE2 Wet & hard STAGE2 Wet & hard STAGE1 Dry & soft STAGE1 Dry & soft Add water Our definition of “hardness” is subside less when being pressed.

5. Preparation 1 To make water mix with the sand evenly, we add some sand and water layer by layer

6. Preparation 2 After putting sand through sieves, we measure the size of sand particle under a telescope

7. Preparation 3 To measure the volume of air in sand, we add water to a cup of sand and press it. volume of air volume of sand Total volume Percentage of air 1mm115.0ml285.0ml400ml28.75% 1mm~ 2mm 178.6ml221.4400ml44.65%

8. Experiment 1 Set Up Counterweights(75g each) syringe A chopstick with scale stabilizer

9. Steps of experiment 1 2. Make sure the top of the chopstick nearly attach the surface of sand 1. Add counter weight to the syringe 3.Release the syringe and measure how deep it sinks into the sand

10. Result of experiment 1 Number of counterweights (cm) Volume percentage of water Depth subsided (1mm sand)

11. Experiment 2 This time we use sand with larger particle (1mm~2mm) to see the difference

12. Result of experiment 2 1mm~2mm 1mm (cm) Volume percentage of water Depth subsided (4 counterweights)

13. Experiment 3 set up A piece of hard cardboard The upper part of plastic bottle container 80 cm

14. Steps of experiment 3 1.Fill the upper part of bottle with sand and cover it with a piece of hard cardboard 2.Remove the cardboard and let the sand ball drop freely 3.Observe the sand ball in the container 80cm

15. Result of experiment 3 A ten dollar coin to compare the size 0%water5%10% 15%20%25% 30%

16. Theory 1st stage: dry and soft Only friction The sand particle will slide easily, and thus softer

17. Theory 2nd stage: wet and hard Uneven cohesions The adhesion will attach water to sand particles, and cohesion of water will pull sand particles together

18. Theory 3rd stage: wet and soft Uniform cohesion Water act as lubricant The cohesion forces affecting the sand particle will be canceled because water covers the sand particle. At this moment, the water will act as lubricant

19. Explanation of Exp 2 In the same proportion of water and sand, more adhesion forces will be formed in fine sand because attached surface is much bigger. Besides, lager distance between sands will stop water from pulling sand particles together.

20. Explanation of Exp 3 25% 30% Air inside make it easy to separate when falling The cohesion and adhesion make it uneasy to separate from the outside

21. Conclusion Percentage of water 1.The sand will be the hardest when water be about to replace the air in it Air in the sand 2.When the air in sand is replaced by water, it will be more difficult to separate from the outside Particle sizes 3. Rougher sand is softer and needs more water to become hard.