Helium-filled+balloons

[|Helium balloons] - helium is lighter than air at ambient temperature, and that explains why helium balloons rise when they are let loose.

Helium-filled balloons are widely used
 * advertising - tethered helium balloons
 * meteorological studies - NASA's Scientific Ballooning Program
 * atmospheric studies - NOAA ozone layer research


 * What do you think?**
 * Have you had a balloon filled with helium? How is it different from a balloon filled with air that you blew up yourself?
 * Why are researchers using helium-filled balloons to lift instruments high above the earth?

> ambient temperature, pressure, gases, density
 * Engineering ideas**

Now it is your turn. Here are some challenges for you to work on...
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..r1d0