Soil Physics 2010

1. Outline • Announcements • Exam • Diffusion Soil Physics 2010

2. Announcements • Exam answers were posted Friday • Exam grades (the circled number 90 ): • Page 2 was the decider Soil Physics 2010

3. Page 2, question 1 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Soil Physics 2010

4. Page 2, question 1 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Soil Physics 2010

5. Page 2, question 1 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Soil Physics 2010

6. Page 2, question 1 Using the bottom of the buckets as the reference height, fill in the table. Distances are in cm. Soil Physics 2010

7. Page 2, question 2 This soil column has a radius of 3 cm, and the outflow is 11 cm3/hr. The values in the diagram are distances in cm. Fill in the blanks: Soil Physics 2010

8. Page 2, question 2 This soil column has a radius of 3 cm, and the outflow is 11 cm3/hr. The values in the diagram are distances in cm. Fill in the blanks: Area = pr2 = 9p ≈ 28.27 , so Soil Physics 2010

9. Page 2, question 2 This soil column has a radius of 3 cm, and the outflow is 11 cm3/hr. The values in the diagram are distances in cm. Fill in the blanks: Area = pr2 = 9p ≈ 28.27 , so Soil Physics 2010

10. Page 2, question 3 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each). Soil Physics 2010

11. Page 2, question 3 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each). Pressure = Total - Elevation No Flow! Soil Physics 2010

12. Page 2, question 3 The system at the right started with dry soil in the column, and it has come to equilibrium. The numbers give elevation in cm, with the bottom of the bottle being the reference height. Complete the table (2 points each). Soil Physics 2010

13. More about diffusion or Both! or • Porosity • Tortuosity • (Constrictivity) • (Continuity) Soil Physics 2010

14. Diffusion: porosity = or Diffusion only takes place in the pores: f < 1 Diffusion only takes place in water: q < f (or in air: e < f) Nothing about pore size! What’s important is the cross-sectional area available for diffusion Soil Physics 2010

15. Diffusion: tortuosity or • Diffusion pathway isn’t straight: • straight distance l • path length l • Ratio l/l is called tortuosity, x • x≥ 1! (gottta be) l l Soil Physics 2010

16. Why is tortuosity squared? or • Suppose l = 3*l • Then the distance a molecule diffuses is 3 times longer: x • But additionally, the gradient is only 1/3 as strong: another x • xxx = x2 l l Soil Physics 2010

17. Diffusion: constrictivity Less important Very important or • Some cross-sectional area doesn’t contribute much to diffusion • Constrictivity isn’t in the equation because we don’t know how to measure it • Often q or e is known, and [tortuosity x constrictivity] is fitted Soil Physics 2010

18. Diffusion: continuity or • Some pores don’t go anywhere: they’re dead ends • Continuity isn’t in the equation because we don’t know how to measure it • Often q or e is known, and [tortuosity x constrictivity x continuity] is fitted Soil Physics 2010

19. Diffusion conclusion or Both! or • Porosity: area, not pore size • Tortuosity: distance ratio squared • (Constrictivity) can’t measure it • (Continuity) can’t measure it Soil Physics 2010