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Science Fair Project on the Weight of Air

Many people have a hard time wrapping their minds around the unseen world. While most people would agree that gravity exists, few would be able to tell you much detail about how it works. The same is true of air. Though we are surrounded by it, and need it to survive, few people realize that it has form, substance, and weight. An educational and eye-opening science project demonstrates that air has a measurable weight.

Experiment Overview
- The objective of this experiment is to answer the question, "does air have weight?" Your hypothesis is to assume that if air has weight, then you should be able to measure it and calculate its density. With that density, you should be able to predict how much air weighs for a given volume. If your calculations are consistent across multiple measurements, you have proven your hypothesis.
Materials Needed
- You should acquire a large poster board upon which to place your hypothesis, data and conclusions as well as a mechanism to create and print them out (a home computer and printer should suffice). You will need a soccer ball, a beach ball, and a medicine ball and a hand air-pump capable of inflating them. You will need an air pressure gauge to ensure each ball is filled to the same pressure. To perform measurements of volume and mass, you will need a tape measure and a sensitive triple beam balance. You should also have a pocket calculator handy to compute volume of the various balls. You may need a flat bowl or dish to keep the balls from sliding off the scale's surface.
Project Process
- You first check the pressure of the soccer ball and beach ball to ensure they are equally inflated to approximately 15 psi (equivalent to one atmosphere), using the hand pump if needed. Measure the mass of each ball three times and record the average to represent the "full mass" of each one. Record the circumference of each ball and calculate their volume using the formula: volume = 4.188787 * (circumference/6.283058) ^ 3. Use the needle from the hand pump to deflate each ball and weigh them again recording the value as "empty mass" in your data tables. Subtract the full mass from the empty mass to determine the mass of the air in each. Divide the mass of each ball by its volume.
Confirming Your Hypothesis
- Measure the circumference of the medicine ball and ensure it is inflated to approximately 15 psi, utilizing the hand pump if needed. With the circumference, calculate the volume of the medicine ball. Multiply the volume by your approximate density for air - this result should be the weight of the air inside the ball. Weigh the medicine ball 3 times and record the average full mass. Remove all air from the medicine ball with the pump pin. Weigh the empty ball three times and record the average empty mass. The result is the actual weight of air inside the ball. Your results should confirm your hypothesis, showing that air has a mass of approximately 35 grams per cubic foot.

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