Saturday, May 24, 2014

What is fog?Science Along the Way

This is the first time we have experienced multiple seasons in a temperate climate in quite a while. It has been fun to watch my children react and enjoy.

This is our front yard Monday morning.  My son wanted to know what that stuff was.  After I informed him that it was fog, he said, "Can I go see what it is like?"  After some observation, he described it as "damp" and "pretty cool".

Both descriptions are accurate.  Fog is a collection of water droplets hanging in the air.

Where did the water come from?

In this case, the water had been there for a couple of days.  Warm air is able to incorporate more water droplets in its mix than cool air.  As long as the sun was heating the earth, the water remained as vapor in the atmosphere.  After dark, the molecules in the air began to loose energy, until it was "pretty cool." When the water molecules loose energy, they may decrease in temperature. They may also change into liquid droplets.  

Why do the droplets float?

Archimedes"s principle: if the mass of the fluid displaced by the object is greater than the mass of the object, it floats. (Remember the Greek guy yelling Eureka?)  The force of the fluid on the droplets is called the buoyant force. So, as long as a water droplet displaces a mass of air greater than it's own mass, it floats.  

When a group of those droplets hang in the air, we call it a cloud.  A cloud near the ground is called fog.  When the droplets join together, they bond tightly displacing less air for the same amount of mass.  The force of gravity pulls them to earth, and we call it rain.

The purpose of this series is to help me, my children, and my readers appreciate the natural world.  If you have found science along your way, I would love for you to share it here. 
E-mail me at for more information.

 Other posts you might enjoy: Cold Blooded Animals on a Cool Day