It's because there are actually two different forces at work here. The merry-go-round effect is caused by centrifugal force, which repels things from the center, while gravity is instead related to centripetal force, which draws things toward the center. ...
2.5. Fluid Actuation: Challenges, and Recommendations for the Extreme POC Actuation of fluid by centrifugal force is at the core of CD microfluidics at the extreme POC. This method of actuation fits well in these applications because of the lack of need for extraneous equipment, power supplies,...