how to calculate a negative acceleration?

Question

I\'m implementing the scrolling behaviour of a touch screen UI but I\'m too tired in the moment to wrap my mind around some supposedly trivial piece of math:

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Answer 1

I have tried this, which works (in Ruby). Not sure if the math is sound but the output looks right, meaning that you get faster as you get towards the center:

velocity=100;
(100.downto(0)).each { |distance_from_black_hole |  velocity=velocity+9.8/distance_from_black_hole; puts velocity; }