Da Vinci’s sketches, which were forgotten for decades, show triangles formed by sand-like particles pouring from a jar. These falling grains depicted experiments to show that gravity was a form of acceleration more than 400 years before Einstein did, a new study argues.
Newton knew it was acceleration too. It sounds to me like he was working with Newtonian gravity, not relativity. Nothing in the article touches on aspects of gravity outside of what Newton had figured out as far as I can tell.