For 2026: Please note that units are considered "under revision" until two weeks before the class date, and page content, web assignments, and exercises may change before that deadline.

Unit 32: Newton's Law of Gravity

Preparation

• History Web Lecture: We talk about a universal law and the concept of physical law.
• Science Web Lecture: The movie demonstrates the derivation of Kepler's laws from Newton's law of gravity and the laws of motion for objects in orbit. Gravity provides a physical explanation for the empirical relationships that Kepler observed. Our quest for understanding how nature works starts with finding patterns in nature, but is not complete until we have identified (when possible) the cause of the patterns we see. Students do NOT need to be able to repeat the derivation but should understand the significance of using mathematical manipulations to predict an observation from a fundamental law.
• Homework: Homework is intended to give students a chance to use the gravity formula. Students should also begin review for next week's review session.
• Discussion: We will go over the derivation from Newtonian mechanics and the universal law of gravity Kepler's law relating the periodicity of a planet to its distance from the sun.

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