1. Questions to ask when reading the textbook section on Descartes 1. What are the two fundamental kinds of reality for Descartes? 2. Which of these does not exist in nature (with one notable exception)? 3.For Descartes matter and motion are two fundamental building blocks of the material world. What image does Descartes use to capture how matter And force are transferred from one place to another? 4. What else cannot exist in material nature in Descartes’ cosmos?

2. Competing systems of natural philosophy Cartesianism Newtonianism Leibnizianism Representatives of each became tied up with the vis viva controversy “God conserves the world in the same action with which He created it.” Nature’s action: Matter colliding with other mattercolliding

3. How to measure “nature’s action.” Descartes - mv Problems: inelastic collisions and the attempt to rescue them Still, the amount of motion would diminish – universe running down

4. 5 slug mass 16 ft Nature’s “action” = force x distance force = mass x accel= 5 x 32 = 160 lb “action” = 160 x 16 = 2560 ft-lb 5 slug mass 16 ft What would be the velocity of the mass when it hit? d= ½ gt 2 = 16t 2 16 = 16t 2 t= 1 v= at = (32) (1) = 32 ft/sec Leibniz’s more “generalized” solution

5. If mv was the measure of the nature’s “action” there was a problem. Not = 2560 mv = 5 x 32 = 160 Descartes must be wrong. Could it be some other combination of 5 and 32? Leibniz proposed nature’s “action” was proportional to mv 2 mv 2 = 5 x (32) 2 = 5120 Proportionality constant = 1/2Vis viva = ½ mv 2 Vis viva is more than a push or pull

6. Newton himself didn’t become involved with vis viva One of his followers, Willem ‘sGravesande, confirmed experimentally that Leibniz’s measure was correct 2 masses of the same size and shape h 2h mass = m mass = ½ m

7. Newton’s reputation was, however, boosted by other events in the 18 th century Controversy over the shape of the earth Doubts about the inverse square law Return of Halley’s comet Secular acceleration of the moon