Apr 14, 2008

Posted by in Motionless Monday | 0 Comments

Motionless Monday: A beautiful red drop of water in slow motion

There is so much beautiful physics in this falling drop of water!

It is especially fascinating because the red color of the water drop helps you visualize the intricate hydrodynamics of the falling drop with the water surface.

You see the real struggle the red drop is going through to stay away from the water. I see three bounces here, each creating its daughter droplet, which in turn bounces back.

So what happens? When a drop encounters a solid surface, its initial spherical shape is forced into a pancake-like form that stretches out over the surface. The kinetic energy of the drop forces it to conform to the planar geometry of the solid surface.

If the liquid in the drop is attracted to the surface, it will continue to spread and eventually adhere to the so-called hydrophilic material. The extent of the spreading is determined by the molecular interactions between the drop and the liquid.

When the molecular interactions between the water drop and the surface are repulsive, water droplets landing on these surfaces try to minimize their contact with the surface.

Thus, after being forced into a pancake shape, the drops retract as they try to re-establish a spherical form to minimize their exposure to the surface. Indeed, for certain cases the retraction can be sufficiently violent that the drop actually rebounds or bounces off the surface after impact

Here you see several attempts by the drop to return to its spherical shape.

More at Physicsworld

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