Ok guys, u can find my animation here:

I’ve got a question: I seem to have two balls bouncing one after the other on the screen instead of one, is it only my impression? If it’s not, what can be the reason for that? Maybe timing?

please guys, don’t leave me alone

have you rendered it out?

The mecanisme of the eye making it possible to create the illusion of movement,persistence of vision, helps us to make the eye perceive
a series of drawings as a smooth movement,
The same mecanisme can also make us see multiple objects or even reverse rotation of what is really happening, - the stroboscopic effect …

The mechanism,- that the eye remembers or hold an impression, , for a small moment of time both help us and makes trouble.
Thin lines with high contrasting background are the worst.
Color fills are less vulnerable. Motion blur helps a lot.
Changing framerate may remove the problem.
Below a link to Wikipedia on the subject:

Best regards