A drop or droplet is a small volume of liquid, bounded completely or almost completely by free surfaces.
The simplest way to form a drop is to allow liquid to flow slowly from the lower end of a vertical tube of small diameter. When the pendant drop exceeds a certain size it is no longer stable and detaches itself. Drops may also be formed by the condensation of a supercooled vapor or by atomization of a larger mass of liquid. The mass m (or weight mg) of the largest drop that can hang from the end of a tube of radius a can be found from the formula
where λ is the surface tension of the liquid, α is the angle of contact with the tube, and g is the acceleration due to gravity. This relationship is the basis of a convenient method of measuring surface tension, commonly used in the petroleum industry.
The major source of sound when a droplet hits a liquid surface is the resonance of excited bubbles trapped underwater. These oscillating bubbles are responsible for most liquid sounds, such as running water or splashes, as they actually consist of many drop-liquid collisions.
The classic shape associated with a drop (with a pointy end in its upper side) is actually an optical effect due to light reflections and the drops rapid movement. The shape of a drop falling through a gas is actually more or less spherical. Larger drops tend to be flatter on the bottom part due to the pressure of the gas they move through.
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Impact of a drop of water.
- 2006-01-28 drop-impact backjet.jpg
Backjet from drop impact.
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A drop of water hitting a metal surface.
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A drop of water hitting a wet metal surface and ejecting more droplets, which become water globules and skim across the surface of the water.
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A drop of water on a leaf.
- Water droplet backjet.JPG
A triple backjet after impact.
- Raindrop on a fern frond.jpg
Photo of a raindrop on a fern frond.
- 2006-01-21 Detaching drop.jpg
Water droplets forming out of a shower head.
- Prosperetti, Andrea (1993). "The impact of drops on liquid surfaces and the underwater noise of rain" (PDF). Annual Review of Fluid Mechanics. 25: 577–602. doi:10.1146/annurev.fl.25.010193.003045. Retrieved 2006-12-09. Unknown parameter
- Rankin, Ryan C. (2005). "Bubble Resonance". The Physics of Bubbles, Antibubbles, and all That. Retrieved 2006-12-09. Unknown parameter
- "Water Drop Shape". Retrieved 2008/03/08. Check date values in:
|Wikimedia Commons has media related to Water droplets.|
- Liquid Sculpture - pictures of drops
- Liquid Art - Galleries of fine art droplet photography
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