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Try This! See How a Thermal Holds Up a Feather

Note: This activity must be done under the supervision of an adult so you don't get burned.

Materials Needed:

  • some feathers; colorful chicken and goose feathers are often sold at craft stores
  • thread or string
  • an electric stove or hot plate burner

Directions:

  1. Tie the feathers with thread or light string to a pencil, ruler, or something else (you can make them into a "dreamcatcher" if you like).
  2. Turn on a front stove burner and wait until it gets hot.
  3. Hold the pencil or dreamcatcher so the feathers dangle at least 8 inches from the burner. Be careful!
  4. Think about these questions: Does the rising heat make the feathers move? Does it hold them up? Would other kinds of feathers work better or worse?
  5. Try the experiment again with feathers of other sizes.

Photo by Laura Erickson

Photo by Laura Erickson

These feathers are hanging
above a cold stove

These feathers are hanging
above a hot stove

If birds and monarchs were weightless, they could rise straight up on thermals (at least if the wind was absolutely calm). But these creatures are not weightless. In order to stay in the air at all when they're not flapping, they must be moving forward. (See our lesson about flight.) And in order to move forward AND stay over a thermal or updraft, they move in a circle. The rising air carries them upwards at the same time. This makes their overall movement a spiral.

In a thermal, eventually the rising warm air cools down enough that it is the same temperature as the air around it. And air rising in an updraft slows down little by little until it eventually dies out. At that point, the animal starts heading in the direction it wants to move. If it is soaring or just not flapping much, it will lose altitude, getting lower and lower, until it discovers another thermal. Then up it goes again!

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