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Hot Air

Find out more about air temperature and pressure , experiment with air, and the answers to trivia questions sent with the kids science project on air.

Trivia Questions

1) What causes hot air to expand?

2) In experiment 2 which balloon expands more? Why?

3) What types of vehicles use hot air?

Find the answers to these kids science questions.


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Science Experiments for Kids Science doesn't have to be complicated, expensive or use specialized laboratory equipment. There are great science projects that can be performed using common household items.

Whether you are a parent or a student trying to find an idea for a science project, a teacher looking for ideas for the classroom, or a science enthusiast who enjoys the delight of experimentation, you'll find what you're looking for in this book.

101 Easy Science Projects



If you have kids, you NEED the Wheel!

Hang the Wheel of Better Behavior on your kitchen wall, and the atmosphere in your home will change overnight. It's guaranteed! Watch the dramatic changes as homework gets done, clothes get picked up, arguing short, the Wheel produces great kids and a stress free environment! The mere presence of the Wheel will have a marked effect on your kids. Chances are, you'll seldom even have to spin it!

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Why does Hot Air Rise?

Warm air rises, and when it rises it becomes cooler. That information is key to understanding a lot of meteorology (science of weather). 

Rising air experiences a drop in temperature, even though no heat is lost to the outside. The drop in temperature is a result of the decrease in atmospheric pressure at higher altitudes. If the pressure of the surrounding air is reduced, then the rising air parcel will expand. The molecules of air are doing work as they expand. This will affect the parcel's temperature (which is the average kinetic energy of the molecules in the air parcel). 

One of the results of the Laws of Thermodynamics is that there is an inverse relationship between the volume of an air parcel and its temperature. During either expansion or compression, the total amount of energy in the parcel remains the same (none is added or lost). The energy can either be used to do the work of expansion, or to maintain the temperature of the parcel, but it can't be used for both. 

If the total amount of heat in a parcel of air is held constant (no heat is added or released), then when the parcel expands, its temperature drops. When the parcel is compressed, its temperature rises. In the atmosphere, if the parcel of air were forced to descend, it would warm up again without taking heat from the outside. This is called adiabatic heating and cooling, and the term adiabatic implies a change in temperature of the parcel of air without gain or loss of heat from outside the air parcel. 

Adiabatic processes are very important in the atmosphere, and adiabatic cooling of rising air is the dominant cause of cloud formation.


Key Points

  • when air rises, its temperature decreases
  • when air subsides, its temperature increases
  • when the temperature of a parcel of air decreases, its relative humidity increases
  • when the temperature of a parcel of air increases, its relative humidity decreases
  • the normal environmental lapse rate applies to still air
  • the dry adiabatic lapse rate applies to rising air, when the relative humidity is below 100%
  • the dry adiabatic lapse rate also applies to air that is subsiding, if there is no moisture present, and no evaporation is taking place

Websites with information on Air Pressure and Air Temperture

Make a hot air balloon
Hilsch Tube
Balloons and blimps

Experiment with a Pin Wheel

Materials - toy pinwheel, pot of boiling water, pot-holder glove

  1. Have an adult boil a pot of water.
  2. With an adult's help, wear a pot-holder glove and hold a toy pinwheel over the steam of the boiling water. Observe what happens to the pinwheel. 
What Should Happen
The heated air molecules from the steam move faster and farther apart. The air becomes lighter and rises upward creating an air current which moves the pinwheel.


Cover for Everything Kids Science Experiments Book

The Everything Kids' Science Experiments Book: Boil Ice, Float Water, Measure Gravity-Challenge the World Around You

Science has never been so easy - all you need to do is gather a few household items and you can recreate dozens of mind-blowing, kid-tested science experiments.

Order Science Experiments Now

  Cover for How Science Works Book

How Science Works

Interesting experiments and good descriptions covering matter; energy, force, and motion; light and sound; air and water; electricity and magnetism; and electronics and computers

Order How Science Works Now

Spa Science

Spa Science

Take science into the bathtub. It's perfect for science fairs, birthday parties and family fun. It will help both girls and boys to think like a scientist in the tub!


Note to Parents:

Creative Kids at Home has checked every weblink on this page.  We believe these links provide interesting information that is appropriate for kids.  However, the internet is a constantly changing place.  You are responsible for supervising your own children.  If you ever find a link that you feel is inappropriate, please let us know. 


Trivia Answers

1) What causes hot air to expand?

Heat increases the motion of air molecules.  The faster molecules move, the more space they use, so as air heats up it expands.

2) In experiment 2 which balloon expands more?  Why?

The balloon on the larger bottle expands more.  There is more air in the larger bottle.  So heating a larger amount of air causes the balloon to expand more.


3) What types of vehicles use hot air?

Hot Air Balloons


Send us a note if you have any questions.




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