[Grady Clay]

“
Manipulated Variable:
Each volleyball has been filled with a different gas.
Three balls?

Responding Variable:
The height to which the ball bounces

Constant Variable:
The ball release apparatus will be the same throughout the experiment.
Each ball will be released from the same height.
The volleyballs are the same brand and size
The pressure of the gas will be constant in all the balls.
What is the precision of the pressure measurement?
The temperature is constant

The balls are filled with 5 pounds of compressed air or helium or nitrogen.
I would use Argon in place of air. With room air, you have uncontrolled water content. You might borrow a tank from a welding shop.
He - 0,1786 g/L @ 0°C, 101.325 kPa.
N2 – 1.251 g/L “
Ar – 1.784 g/L “

The balls were dropped 10 times each.
I would do this more times depending on the “placebo” experiment below.

This is our release device. Shop vac when turned on would hold the ball, when switched off the ball would drop.

How are you going to measure the height of the bounce? How accurate is that measurement. How repeatable are the measurements? A useful way to measure this is to use a video camera to view the ball at the apex of the bounce and a meter stick in the background. Then view the ball frame-by-frame.

The person measuring the height should not know what gas is in the ball or what order the drops are. Double blind.

A useful “placebo” experiment would be to do the experiment all the same gas in the three balls. Number the balls. Is there any difference between the balls?

Another useful experiment is to run the experiment with the pressure from 4.0 to 6.0 psi and determine the effect the pressure has. This will tell you how sensitive the experiment is to pressure. You could also do this with temperature.

For an 11-year old, the most useful things to focus on might be;
Effect of bias.
Accuracy of measurements (including the effect of parallax with the camera).
Why you do many repetitions.

A useful way to analyze the data is using your Post-Its on a number line marked with appropriate equal intervals. For example, if 5.0 cm intervals are appropriate and you had three results; 2674 cm, 2672 cm and 2674 cm. In the interval between 2670 and 2674 (inclusive), you would paste on the Post-Its to build a vertical bar. With enough data points, this generates an understandable histogram. You can talk about the average (mean) and how sharp or flat (standard deviation) in a visually understandable form. Using Post-Its allows your student to build the curve data point by point.


The wonderful thing about science fair is it allows you to include so many important things in a fun project. In 1st and 2nd grades my youngest did; “”Do un-stretched rubber bands shoot farther than pre-stretched rubber bands?” and “Do big water balloons go farther than little ones?”

Best,
Grady