[Coda]

If the object is spinning at a constant angular velocity, then the net force acting on that object is directed towards the center of rotation. If the object is speeding up, then you have that force as well as a (straight-line) force going straight forward that's causing the object to accelerate.

In practice you still have to apply a force going forward to keep an object spinning due to energy loss from air resistance, friction in the rope, etc. But the net tangential force is zero if it's spinning at a constant rate.

The colon is a fairly weak choice there. You COULD use a dash, a colon, a comma, or parentheses in that context. Each one has a slightly different nuance. Parentheses, for example, deemphasize their contents relative to the sentence, and you could take the contents out without impacting the meaning. A comma suggests that the clause that follows describes the noun before the comma. A colon suggests that the part afterward specifically follows from or equates to the idea introducing it. And a dash would function like parentheses except with stronger emphasis. These aren't hard and fast rules, and my interpretations of them are certainly not the only way to look at them, and you definitely shouldn't try to read too much into a statement based on its choice of punctuation.

A semicolon wouldn't have been wrong in that context but a period is better because the connection between the two thoughts isn't especially strong. Either sentence is strong on its own without need for further information.