What is the life span of raindrops?

[MorkandMindy]

I just asked myself this one today and I can't answer it.

 

[Washington]

The bottom of a rain cloud is typically no more than 6,500 feet high, and depending on size of the drop (.5 mm to 5 mm), they fall at a speed of 4-20 mph. So, their life span is anywhere from 3.7 to 18 minutes. The larger the drop the faster it falls.

 

[MorkandMindy]

Wow, I like that answer

I didn't know the bottom of a rain cloud was unlikely to be higher than that

and yes, it's just started to rain outside.

and I feel a harder question coming on...

 

[UnafraidOne]

The bottom of a rain cloud is typically no more than 6,500 feet high, and depending on size of the drop (.5 mm to 5 mm), they fall at a speed of 4-20 mph. So, their life span is anywhere from 3.7 to 18 minutes. The larger the drop the faster it falls.

Don't the drops form some time before they fall?

Why do larger drops fall faster?

 

[Washington]

Don't the drops form some time before they fall?

In a sense yes. They start out as accumulations of water vapor around very tiny particles of dust. When they reach a critical size, which varies depending on several factors, they began falling. For reasons that are still not completely understood often they quickly begin bonding with each other to form larger and larger raindrops. Larger drops may also form inside clouds where eddies of air currents keep them aloft during their bonding until conditions moderate or they become too heavy and they start to fall. In some cases, during their descent the drops may start to evaporate and be much smaller when they reach the ground. And sometimes where the evaporation is total the drops will disappear and never reach the ground. Such rain is called virga

Why do larger drops fall faster?

Because they weight more. Although their surface dimension increases as their size grows it does not match the increase volume that takes place. Consider: A sphere with a diameter of 2 has a surface area 4 times that of a sphere with a diameter of 1, whereas the volume of the larger sphere will be 8 times larger, and hence is much heavier. In short, the increase in air friction due to the increase in surface dimension is more than off set by the weight of the far greater increase in volume.

 

[UnafraidOne]

Because they weight more. Although their surface dimension increases as their size grows it does not match the increase volume that takes place. Consider: A sphere with a diameter of 2 has a surface area 4 times that of a sphere with a diameter of 1, whereas the volume of the larger sphere will be 8 times larger, and hence is much heavier. In short, the increase in air friction due to the increase in surface dimension is more than off set by the weight of the far greater increase in volume.

In a vacuum a feather and a rock fall at the same rate.

 

[Washington]

In a vacuum a feather and a rock fall at the same rate.

That's correct.

 

[Wiccan_Child]

In a vacuum a feather and a rock fall at the same rate.

If we lived in a vacuum, we wouldn't have raindrops in the first place .

 

[Wiccan_Child]

The bottom of a rain cloud is typically no more than 6,500 feet high, and depending on size of the drop (.5 mm to 5 mm), they fall at a speed of 4-20 mph. So, their life span is anywhere from 3.7 to 18 minutes. The larger the drop the faster it falls.

For some reason I can't rep this post. Higher powers are at work...

 

[Washington]

For some reason I can't rep this post. Higher powers are at work...

Thank you. It's the thought that counts.

 

[Madcoil]

Raindrops die when they hit the ground?

 

[UnafraidOne]

That's correct.

??

If a feather and a rock fall at the same rate in a vacuum then that would
imply that their mass difference has nothing to do with their rate of descent. Right?

So then this statement you made about the heavier drops is false: "In short, the increase in air friction due to the increase in surface dimension is more than off set by the weight of the far greater increase in volume." (bolding and italics mine)

 

[UnafraidOne]

If we lived in a vacuum, we wouldn't have raindrops in the first place .

 

[Wiccan_Child]

Raindrops die when they hit the ground?

It's all part of the Great Hydrocycle of Life.

 

[Tiberius]

owever, the water within the raindrops is ancient. It's entirely possible that the water in a raindrop fell on the battlefields of World War One, it may have been part of Cleopatra's bath one day, and may have been drunk by dinosaurs, and was almost certainly part of the oceans when the first life was arising on this planet. Remember, water isn't created or destroyed (in general, it is possible, but that requires human intervention for the most part), but it keeps going round and round in the hydrological cycle.

 

[Washington]

??

If a feather and a rock fall at the same rate in a vacuum then that would
imply that their mass difference has nothing to do with their rate of descent. Right?

So then this statement you made about the heavier drops is false: "In short, the increase in air friction due to the increase in surface dimension is more than off set by the weight of the far greater increase in volume." (bolding and italics mine)

It all has to do with terminal velocity.

Here is a site with an explanation and that also lets you experiment with the velocity of various size raindrops. Just move the rain drop cursor up or down on the scale to change the size of the rain drop.


http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=146

 

[UnafraidOne]

It all has to do with terminal velocity.
Here is a site with an explanation and that also lets you experiment with the velocity of various size raindrops. Just move the rain drop cursor up or down on the scale to change the size of the rain drop.

It appears I was wrong. The mass difference does become a factor when other forces are involved. Thanks for the link.