Amergin wrote:It has been raining today heavily. I have sat on my patio watching it. Along the eaves water gathers and then drips. I watch the water build until eventually it falls. Now clearly surface tension and mass dictate size of drips like this. Does anyone know the optimum size i.e. volume and mass or volume and weight? On other planets with less gravity or more this must effect the size. Any answers??

Amergin wrote:Is thyere a range of values? They seem pretty much the same size as I watch them fall?
Seriously.

Amergin wrote:
On other planets with less gravity or more this must effect the size. Any answers??

Templeton wrote:

Amergin wrote:
On other planets with less gravity or more this must effect the size. Any answers??

Gravity isn't constant on earth. Don't know whether the difference is significant enough to alter rain drop size

Amergin wrote:The situation I am acually wondering about is the drop of water at the end of a tap for instance where the washer is inefficient. The water gathers at the taps rim and then falls -often the dripping is quite regular. At the moment of it detaching itself it must be its weight that, under gravity, makes it fall. What is the weight and volume of the drop at that point. Given that gravity varies on our planet what is the range of weight/volume of the drop. Mineral content of water will be involved so volume will vary there but not weight.

In the pendant drop test, a drop of liquid is suspended from the end of a tube by surface tension. The force due to surface tension is proportional to the length of the boundary between the liquid and the tube, with the proportionality constant usually denoted γ.[1] Since the length of this boundary is the circumference of the tube, the force due to surface tension is given by



where d is the tube diameter.

The mass m of the drop hanging from the end of the tube can be found by equating the force due to gravity (Fg = mg) with the component of the surface tension in the vertical direction (Fγsinα) giving the formula



where α is the angle of contact with the tube, and g is the acceleration due to gravity.

The limit of this formula, as α goes to 90°, gives the maximum weight of a pendant drop for a liquid with a given surface tension, γ.



This relationship is the basis of a convenient method of measuring surface tension, commonly used in the petroleum industry. More sophisticated methods are available when the surface tension is unknown that consider the developing shape of the pendant as the drop grows

Amergin wrote:I am grateful. I will not work it out either but it will be in my head when it rains again as it is supposed to do tomorrow.

Amergin wrote:many grateful thanks for your troubles and time.