Plants Use Capillary Principle of Physics to Survive

Dr. Cameron Ahmad
3 min readMar 30, 2021

The falling of apple noticed by Newton made him pen down the Law of Gravitation (it will be discussed in another blog). As a result, we experience everything that has a mass gets attracted towards the earth. The force of attraction it experiences is towards earth as its mass is too small in comparison to that of the mass of the earth being ~ 6 x 10²⁴ Kg. This law gets also confirmed when all fruits bearing trees, have their fruits growing in size in the direction of the earth!

So, how can we take a bucket of water from its ground level to the top of the Big Ben clock in London whose height is 288 ft? The oldest way is by physically filling a bucket on its ground floor, then carry it by stairs. But by the time one would reach the top, one would be sweating, out of breath, and exhausted. This happens as one has to work against the force of gravity told to us by Newton above while taking the bucket to the top. Alternatively, today we can have a water pipe, connect it to a pump and make the water reach the top level to fill our bucket there. Here the same work against gravity will be done by a pump. But what if there is no pump and no one carries the bucket of water. Can water still reach by itself to the top? That too continuously against gravity. Is your answer NO?

Think again as Physics not only has a living example around us through its principles defying it, but it happens 24x7x365 in trees which “pump” (if I am allowed to use the same phrase); to ensure water, food, and nutrients reach its branches and leaves at a height higher than that of the Big Ben clock! The tallest trees found on earth are of Hyperion having a height up to 342 ft found in coastal California, USA!

Source: Tallest Tree is Higher Than Big Ben …

We breathe oxygen continuously even while sleeping and breathe out carbon dioxide along with several other living organisms on this earth. Trees and shrubs recycle carbon dioxide by converting it into oxygen in our environment for our survival. So for trees to survive they require water to reach its topmost level continuously as well. How?

Just above we learned for anything to be moved against the gravitational force of attraction it will require a greater amount of force to be exerted resulting in doing work against gravity. So, do we see tall trees have any pump beside them to push water, food, and nutrients to their topmost branches and leaves? No! Then how does this miracle happen 24x7x365? The answer to it can be found in Physics laws and principles.

There are three physical phenomena in our daily life that make it happen. The first is Surface Tension. For example, we find the surface of water formed in a thin glass tube/straw, is concave; on the other hand, in the mercury-filled thermometer used in our homes and in the case of oils they have a convex surface. The formation of surfaces in such a manner is as a result of the Molecular forces of attraction (as per the Law of Gravitation) which make the surfaces concave or convex shape for water, oil and mercury. The second thing which plays a vital role is Viscosity and finally, the diameter of the Capillary tube. All three work in a combination to result in liquid rising against the gravity in a capillary tube.

In very simple terms the Jurin’s Law helps us to determine the height h of a column to which a liquid may rise. If it is assumed all other terms are constant in this law, then the height h is inversely proportional to the diameter (radius) of the capillary tube viz.,

h ∝1/r

So, as the cross-section of the capillary tube decreases, the height by which liquid will rise will increase. The normal veins in plants that carry water are of the order of 100 μm or 100 x 10^–6 mm. Hence a tree-like Hyperion has veins in whose diameter decreases even further to be able to lift water to such a great height against the force of gravity!

Cameron Ahmad

Code: PHSK-3

March 29, 2021

Brampton ON




Dr. Cameron Ahmad

B. Sc (Hon) in Physics, M. Sc (Biophysics & Electronics). M. Tech (Applied Optics), PhD (Engineering Science), PMP, RDCS, DMS, CET, AScT, CTDP & CECC