Solar Bag Experiment (Harness the Power of the Sun)
The amazing 25 ft long floating bag!
A Solar Bag is a long plastic bag made from a very thin plastic and colored black to absorb solar energy. The heated air inside the bag provides buoyancy and causes the bag to float. Over the years, it’s become a very popular science demo for teachers to share with their students as they explore the properties of air.
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- Solar Bag
- Solar Bag String
- Packing tape (for repairs)
- Adult supervision
Select the best time and conditions for a launch:
- The best time for a launch is in the morning when the temperature of the air outside is cool. We have not had much success with a launch attempt in the middle of a hot day.
- Select an appropriate location for the launch. Find a park or an open field clear of any buildings, trees, and power lines to conduct the launch.
- Select a day to do the experiment when it’s sunny and free of any wind.
Carefully remove the plastic bag from the packaging. Notice that the bag is made out of a lightweight plastic material. Use caution when handling the bag since the plastic will tear easily.
Locate one of the open ends of the bag. Tie a knot in this end of the bag.
Unroll the Solar Bag onto a soft surface like grass. Avoid pavement or gravel since the plastic material can easily tear. Have one person hold the bag open as you begin to run around and scoop up air. Believe it or not, you can inflate the bag in just a couple of minutes.
Fill the bag by shaking it open loosely, and gently running with it to scoop up the air. Add air until approximately 2 feet of deflated plastic remains in your hand. Slide your hand along the plastic to make sure that the air in the inflated portion of the bag is stretching the plastic tight.
HINT: It helps to have two people support the bag as you work to fill it, to avoid any tears or snags on the ground.
Tie a knot in the open end of the bag. Then, tightly tie the Solar Bag String around the knot. Hold tightly to the other end of the string, or tether it to the ground.
Watch as the sun heats the air in the bag and it begins to float. Adjust the length of the string to allow the bag to rise or fall, just be careful not to let go of it.
Be careful when deflating the bag at the end of your flying adventure. The outside of the bag as well as the air inside may be hot.
How Does It Work
The remainder of the work is done by the sun. You may notice that the outside of the bag gets hot, but what is happening to the gas molecules inside the bag? As the sun warms the air molecules in the bag, their movement begins to speed up. Since the heated air inside the bag is less dense than the cooler air on the outside of the bag, the Solar Bag will float. It’s important to remember that it may take as long as ten minutes for the air inside to heat up enough to cause the bag to float.
Storage and Repair
We store the deflated bag in an old pillow case, which helps prevent accidental punctures or tears when it’s not being used. If a small tear is spotted, clear packing tape can be used to repair the damage.