Does using a swimming cap make a swimmer swim faster?
The hypothesis holds true: the participants swam faster when they wore caps. They swam more slowly when they did not wear caps.
A swimming cap is an important part of one's swimming attire. It improves the performance of a swimmer because it reduces the degree of drag on the swimmer. It also protects a swimmer’s hair from the chlorine in the pool and keeps a swimmer warm.
Get participants to wear swimsuits that are made of different materials.
If your participants are game, have them shave the hair on their bodies (eg. armpits, legs, and observe the difference in results).
How to choose a cap and goggles for competitive swimming? - http://www.ehow.com/how_2318119_choose-cap-goggles-competitive-swimming.html
Competitive swimming caps - http://www.swim2000.com/page.php?p=competitive-swimming-caps
Ensure that all of the participants are confident swimmers and have a life-guard on standby at all times.