  Concerning the motion of projectiles, gravitational acceleration, and the motion of celestial bodies, Albert adopts Buridan’s major innovation, i.e., the theory of impetus, a quality acquired by a moving body (see Buridan’s Questions on the Physics VIII, qu. 13, on projectile motion). Like Buridan, he extends this approach to celestial bodies in his commentary on De caelo, clearly following its consequences in rejecting intelligences as agents of motion and in treating celestial and terrestrial bodies using the same principles. Nevertheless, he formulates the idea of impetus in more classical terms as a virtus impressa (impressed force) and virtus motiva (motive force). Albert makes no pronouncements about the nature of this force, claiming that this is a question for the metaphysician. His work also mentions the mean speed theorem, a method of finding the total velocity of a uniformly accelerated (or decelerated) body, which had been stated (though without being demonstrated) in Heytesbury’s Tractatus de motu, and also adopted by Nicole Oresme. Albert was part of a general scientific trend which sought the first formulations of the principles of dynamics. He explained a number of curious natural phenomena, taking particular interest in earthquakes, tidal phenomena, and geology.