Four friends are sitting on a rotating roundabout. The red friend can throw a ball towards the centre of the roundabout (use the "Throw ball" button) with an adjustable velocity. The left-hand image shows the view from above, from a camera that is fixed in space relative to the ground. The right-hand image shows the view from above, from a camera that is fixed to the roundabout.
The small red line on the red friend shows the initial velocity vector of the ball as it is released. In order to make the ball go directly through the centre of the roundabout, you will need to cancel out the tangential velocity: the red friend needs to throw the ball towards his right since he is moving towards his left.
The ball travels in a straight line through space (as you can see on the left-hand image), but to observers who are rotating with the roundabout (the right-hand image) it appears to travel through a curved path.
See if you can play with the parameters to make the ball pass directly through the centre, return to the thrower, hit one of his friends, stay completely still, or do several laps before exiting.