Material density and the transmission of sound
The hypothesis that higher density materials will transmit less sound, is proven to be true. Higher density materials act as very good sound barriers.
Sound barriers are used to protect homes that are located near airports, highway and train lines, from noise pollution. It helps to improve the quality of life for the people who have been affected by these noise pollutions.
To improve the reliability and accuracy of our results, a larger sample of participants should be used.
This science fair project may be repeated, this time, comparing different elastic materials like rubber, metal, etc.
Modify the science project experiment, using different sources of sound like a portable CD player.
Noise barrier - http://en.wikipedia.org/wiki/Noise_barrier
The speed of sound in other materials - http://www.ndt-ed.org/EducationResources/HighSchool/Sound/speedinmaterials.htm
Handle breakable/heavy materials carefully. Ensure that you wear protective gloves.