1. Soil Physics 2010 Outline Reminder Where were we? Capillarity

2. Soil Physics 2010 Reminder Homework 1 is due

3. Soil Physics 2010 Uh-oh Quiz

4. Solutes lower the water’s energy Soil Physics 2010 Fresh water Salt water Water moves from higher (pure) to lower (salty) energy state Where were we?

5. How do we know it’s energy? Soil Physics 2010 Fresh water Salt water At equilibrium, the higher pressure balances the energy-lowering effect of the salt. hh This is the osmotic pressure, 

6. Soil Physics 2010 Water and heat Water is resistant to temperature change, including phase change Heat capacity in J/kg, liquid: Methane 4022 Ammonia 4708 Water 4186 HF 2580 Neon 2009 H2S 2509

7. Soil Physics 2010 Capillarity demoroom.physics.ncsu.edu

8. Soil Physics 2010 Cohesion

9. Soil Physics 2010 Cohesion If each water molecule has the same cohesion, then molecules on an interface cohere preferentially inward and along the surface.

10. A floating body (length 2.5cm) contains a small volume of soap, which serves as its fuel in propelling it across the free surface. The soap exits the rear of the boat, decreasing the local surface tension. The resulting fore-to-aft surface tension gradient propels the boat forward. The water surface is covered with Thymol blue, which parts owing to the presence of soap, visible as a whitish streak. From John Bush, MIT A soap boat Soil Physics 2010

11. Surface tension Interfacial tension Surface energy One effect of surface energy is to minimize the surface area

12. Soil Physics 2010 Surface tension One effect of surface energy is to minimize the surface area

13. Soil Physics 2010 Adhesion But also: Water “sticks” to other materials, not just to itself

14. Soil Physics 2010 Capillarity Bloody2.com demoroom.physics.ncsu.edu

15. Soil Physics 2010 Capillarity At equilibrium, Force up = Force down Force = Mass * acceleration (Newton’s 2 nd law) Force down= mass * g =  w (  r 2 h) * g (or better) = (  w –  a ) * (  r 2 h) * g r h

16. Soil Physics 2010 Capillarity At equilibrium, Force up = Force down r Force up =  * 2  r Force up is: proportional to surface tension  exerted around the inside perimeter of the tube

17. Soil Physics 2010 Capillary rise equation At equilibrium, Force up = Force down Force down= (  w –  a ) * (  r 2 h) * g r h Force up=  * 2  r (  w –  a ) * (  r 2 h) * g =  * 2  r

18. Soil Physics 2010 Wetting angle www.alsapaint.com

19. Soil Physics 2010 “A raindrop is extended like a film by water processing on the surface of a mirror, and the visibility in case of rainy weather is raised.” Honda ad, honda-car.jp www.croda.com Changing the wetting angle