Unit 30: Newton's Laws of Motion

Preparation

• History Web Lecture: Newton's Laws of Motion mark the end of Aristotelian mechanics in the west. It is important for the student to see not only how the concept of force has changed, but how the use of mathematical analysis created a mechanical world view in which all motion could be analyzed and future positions determined. The idea that some future state (position of all objects and their current motions) could be calculated if we had enough information about our current state is called determinism. An extreme interpretation of determinism would imply that we have no free will, so Newton's ideas created a debate in science and religion on the limits of knowledge and the possibility of moral action in a deterministic universe. In the early twentieth century, work in quantum mechanics led to the realization that we cannot know precisely what bodies, especially small components of atoms, are actually doing enough to determine their precise location and motion. The debate remains, however, whether our inability to predict future states is a limit only on our knowledge, leaving us still inhabitants of a completely determined universe.
• Science Web Lecture: The web lecture introduces Newton's three laws of motion and the mathematical nature of the second law, then suggests how these apply to a specific situation. Changing the direction of flight of a rocket may seem to contradict the law of inertia, unless we realize how a system is defined as a collection of objects with a center of mass.
• Homework: The history section of the homework reviews some of the differences between Newtonian and Aristotelian mechanics. The science section asks students to attempt some practical applications of the Newtonian force laws. If necessary, help the student with the mathematics: the point is not so much to learn mat as to understand that the math accurately describes the situation. We have a new technique for understanding and predicting natural events.
• Discussion: Our discussion will focus on the definition of force, particularly the concepts of proportionality and dependence (increasing force increases acceleration).

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