• Question: How does water travel up the trunk of a tree, since it is not following gravity?

    Asked by anon-244324 to Ondrej, Jordan, Eleanor, Ed on 19 Mar 2020.
    • Photo: Jordan McElwee

      Jordan McElwee answered on 19 Mar 2020: last edited 19 Mar 2020 7:52 am

      Really great question. I think I once read about this, but if I’m wrong I apologise! Trees have thin tubes in them which the water can travel up, in a process called capillary action. This process describes the flow of a liquid in a thin tube against gravity. There are 2 things that cause this: cohesion and adhesion.
      Cohesion describes the attractive force between similar molecules, in our case the water.
      Adhesion is the force between dissimilar molecules, so the walls of the tube.
      With adhesion, the water molecules are attracted to the walls of the tube and can ‘climb up’, therefore allowing the water to travel upwards. I’m sure cohesion will have something to do with it too.. but I’m not certain. The fact it’s a thin tube is important, as you have a higher surface area between the tube and the water. Pretty neat!

    • Photo: Eleanor Jones

      Eleanor Jones answered on 19 Mar 2020:

      I remember this, Jordan! Always thought it was a pretty cool trick!

    • Photo: Ondrej Kovanda

      Ondrej Kovanda answered on 19 Mar 2020:

      As Jordan pointed out, this effect is called capillary action. Essentially, the liquid’s desire to stick to a wall of a tube becomes greater than tit’s desire to obey the gravity, provided that the tube is very thin.

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