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SCV Outdoor Report: So Many Raindrops

By: Wendy Langhans


ImageWhen we think of raindrops, we often picture a dripping faucet with tear-shaped droplets.  But in the natural world, raindrops are NOT tear-drop shaped.  Furthermore, the shape of raindrop varies according to its size.  Small drops, those with less than a 1 mm radius (roughly the diameter of a straight pin), are spherical.  As drops grow in size they begin to resemble a hamburger bun, flat on the bottom and round on the top.  After they reach a size of about 4 mm in diameter, they break apart into smaller drops.

So why does the shape change with size?  

It has to do with the opposition between two physical forces:  surface tension and air pressure.  Surface tension is the tendency for a molecule of water to be pulled back into the liquid.  Water molecules inside the drop are pulled at from all sides, while those at the surface are pulled sideways and inward.  Since the tension at the surface is equal on all sides of the water droplet, you get a spherical shape.

To understand the force of air pressure, imagine you are driving in a convertible with the top down.  (Personally, I like to remember the times when my soon-to-be husband took me out for a spin in his Fiat convertible.  But that’s a story for another day.)  You don’t see the molecules of oxygen and nitrogen in the air, but you certainly feel them.  As a water droplet falls through the air, it too is hit by these air molecules.  The larger the water droplet, the greater the terminal velocity and the more air molecules it bumps into as it falls.  These collisions flatten the droplet into the shape of a hamburger bun, sometimes even giving it a dimple on the bottom.

This gives us a whole new way of looking at a “Big Mac”, doesn’t it?  

ImageUpcoming Outdoor Events:  (Remember, heavy rain cancels MRCA-sponsored events)

Twilight Walk at Towsley Canyon. Saturday, Jan. 12, 3:30 – 5:30 PM.  
Sponsored by the Mountains Recreation and Conservation Authority.

Click here for a map. 

Placerita Canyon Nature Center Docents’ Bird Walk. Saturday, Jan. 12, 9:00 AM.  

For more information call the Nature Center a 661-259-7721.

Trail Maintenance Volunteers at Towsley Canyon. Saturday, Jan. 12 and 26, and every Wednesday, 8:00 AM.   Come join our trail maintenance volunteers for camaraderie and a heart-thumping workout.  

For more information call Steve Ioerger at 661-291-1565 or
Sponsored by the Mountains Recreation and Conservation Authority.

Weekday Wanderers Bird Walk at Towsley Canyon. Tuesday, Jan. 15, 9:00 AM.  

Sponsored by the San Fernando Valley Audubon Society.For information contact Carolyn Oppenheimer before 7:00 PM at 818-885-7493 or

Click here for a map.

You can listen to stories like this every Friday morning at 7:10 a.m. on "The Hike Report", brought to you by your hometown radio station KHTS (AM1220) and by the Mountains Recreation and Conservation Authority.

For the complete MRCA hike and activity schedule and for trail maps, go to

SCV Outdoor Report: So Many Raindrops

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