Near perfect.
As the design is concerned, it's all right for me ;o))

But in the first experiment, is it possible to let a trace of the ball after make it goes up (I mean a circle in dot line to see that when we will let it fall, it'll go at the same place) ?
And a moving square to show that the trace is perpendicular to the ground.

I'm wondering too if it's possible not to see displacement by default.

And I would like to translate the name of the tabs (Replace Experiment 1 and 2 by Expérience 1 and 2) but they don't appear in the GUI translation tool ;o((