This
phenomena can be explained by Brownian motion, which is the random drifting of
particles in a liquid. The kinetic
theory states that all matter is made out of particles which are in constant
motion in proportion to their energy and attraction between other particles. A
particle can consist of atoms, molecules or ions.
In water or
other liquids the attraction between the particles is relatively low, which
means that the water molecules can move freely. The grains of pollen move due
to the water particles bumping into them causing movement. This is a random
physical occurrence, which means that the water molecules can hit the grains of
pollens from different directions at any time.
The
observation of grains of pollen moving in a random motion on water was made in
1827 by a botanist called Robert Brown.
Below is a demonstration
of Brownian motion. The red particles represent grains of pollen (out of proportion) being moved around by the blue water molecules.
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