See How Warm Air Expands with Project Weather School

LOUISVILLE, Ky. —We are heading back to school with meteorologist Chris Havely this week.  Chris explains why and how warm rises and cold air sinks.  Here are a few things you will need for the experiment.

What You’ll Need:

  • plastic water or pop bottle
  • large bowl or Tupperware 
  • balloon
  • ice water
  • hot water

Instructions:

  1. Fill the plastic bottle with hot water then pour it out.
  2. Then fill the bottle a quarter full with hot water and place the balloon over the bottle.
  3. Fill the large bowl with ice water and place the bottle in the bowl.
  4. Watch as all of the air is taken from the balloon and sucked into the bottle.

What Happened:

The hot air in the bottle expands as the cool air outside the bottle contracts. When you first place the balloon over the mouth of the bottle, the air in the bottle is hot. As the air cools from the ice water outside the bottle it contracts and pushes the balloon into the bottle. This is why the air is taken from the balloon and sucked into the bottle.

Warm air expands because the molecules are moving more and spreading out.  This causes it to be less dense and thus why warmer air will rise and cooler air will fall.