Why do water droplets form on the outside of a cold glass?

Robert Jackson

Have you ever wondered why a glass of cold water sometimes has water droplets on its outer surface? Is the glass broken? Well, there is nothing wrong with your glass and it doesn’t leak water. The reason for the droplets occurring lies in the temperature difference between the glass and the air.

Your glass doesn't leak water

It might sound weird, but water is omnipresent. The air around you is full of water, you just don’t see it because the water is in the form of a gas called water vapor. Even though you might not see water in the air you can still feel it. The level of humidity might affect your sense of comfort.

Just like all matter, water moves from one state to another if you change its temperature. Think about the freezer in your refrigerator for example. It’s really cold in there and water turns into ice. Water at room temperature stays in liquid form, but if you start boiling it you’ll see vapor escaping from the water surface and dissolving into thin air!

Now, let's go back to our “sweating” glass of cold water. What's really happening here is called condensation, it’s the opposite process of evaporation. When water vapor in the air meets something cold it gets cooled and turns into liquid droplets again! That’s why your glass of water gets wet on the outside.

Condensation can be observed everywhere where temperature changes occur. Think about your bathroom mirror getting misty when you take a hot shower. What about dew drops on the grass in the morning? The grass is getting cooled down during the night and when the sun rises in the morning it warms up the air again. The air comes into contact with cold blades of grass and forms those beautiful dew drops!

Did you get it?
13 Votes
  1. User profile picture

    That’s brilliant!