Frost vs. Dew

This activity helps demonstrate the difference between frost and dew and how each forms. Click here to watch my video demonstration, and at the end of this post, you can see the time-lapse of the experiment!

What you need: 

• 2 tin cans (remove the labels and lids)

• Salt

• Ice

• Water

What you do: 

• Fill each can about half way with ice. Crushed ice works best because you have less empty space in the can, but cubes can work too. 

• In the can where frost will form, add about 4 tbsp salt and mix well. It doesn't have to be exact; if you're estimating, it's better to add too much than not enough.

• In the can where dew will form, pour in enough cool water to cover the ice

• That's it! This doesn't happen right away, so this can be a great time to teach your lesson while you wait for the reaction to play out. Or you can set up a time lapse to capture what happens. 

What is happening: 

Salt helps melt ice (click here to see my experiment and explanation as to why this happens - it can be a great companion to this experiment!). Melting requires heat, so it pulls heat from the atmosphere around it which makes the atmosphere cooler around it. Cooling the atmosphere causes the little particles of water vapor in the air to condense onto the surface of the can. The mixture in the can is colder than freezing, so the water that collects on the outside of the can is frozen. 

In the other can, the water and ice combination is around 32º and the temperature outside the can is warmer than that. Liquid collects on this can because the reaction we talked about on the other can isn't happening.