Objects travelling along a curve

Hi all,

I'm having trouble getting objects to travel along a curve which slopes in all kinds of directions.

As you will see in my Grasshopper-sketch, I've used two forces, a UForce and a CurvePull to make the points travel while adhering to the line. However, when the points reach the point on the curve where they have to start turning, they sort of stop, and just start revolving around themselves. I suspect this is due to the UForce not changing, so I guess my question is:

How do I continuously change the UForce so that it corresponds with the 'direction' of the curve? Or if anybody has a better idea, I'd be happy to hear. In advance, thanks!