Balloons

Hot air and helium have lower density than cold air, so balloons filled with these are "lighter than air".
 * [|density] - An object with a lot of matter in a certain amount of volume has high density. An object with a little matter in the same amount of volume has a low density.
 * temperature has an effect on density. When the temperature of a substance increases, the density decreases because the atoms are moving all around the place having less mater in one space.

Uses
 * weather, scientific research
 * transportation

[|Crazy Lawn Chair Balloon Flight!] (video 4:01) - John Freis, 51, ties 170 helium balloons to his lawn chair (in a sophisticated manner, of course) and flies up to 12,400 ft, traveling 46 miles in almost 4 hours. He had a parachute, oxygen, GPS, ballast and a BB gun.
 * What's the problem?**
 * **Ask** - Hot air balloons are used to carry people up into the air, they require large specialized fabric envelopes, large gas-powered burners to heat the air to create the necessary lift. Is it possible to achieve the same experience on a small scale one-time ride using only helium-filled balloons? What would be needed to produce enough lift? How would you do this?
 * **Imagine** - Using helium-filled balloons eliminated the need for the weight of the burner, basket and envelop of the hot air balloon. How would these be replaced? How would the pilot get back down?
 * **Design, Build** - How much did the framework, chair and pilot weigh? How much weight could a single helium-filled balloon lift? How many balloons would be required? How would these be attached to the structure? How many people were needed to do the work of setup?
 * **Improve** - Is there a better way to do this? What would they do differently next time?


 * That's engineering**
 * [|helium] - a chemical element. Astronomers discovered helium in 1868.  It is called a noble gas, because it does not regularly mix with other chemicals and form new compounds. Helium is used to fill balloons and airships because it is lighter than air, and does not burn or react, meaning it is normally safe for using it in that way.
 * [|atomic number] of an atom is the number of protons in the nucleus of the atom. The atomic number of an atom defines which element it is. In a neutral atom, the atomic number is equal to the number of electrons orbiting the nucleus. The elements of the periodic table are listed in order of increasing atomic number.

> helium, altitude, oxygen, GPS, ballast, lift, noble gas, react, burn, atomic number
 * Engineering ideas**

Challenges for you to work on...
 * Do It**
 * Using a helium filled balloon, explore its lift capabilities, by suspending different small objects from the balloon. Hang on to the string, so the balloon doesn't get away. How much weight can the balloon lift? Does that seem like a lot? How many balloons would it take to lift you?


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