AST 101 Lecture 5: AST 101 - Lecture 5
Document Summary
Newton knew this law was consistent with his laws of motion, and with the observed behavior of falling objects near the earth"s surface (local gravity). What he was really after was a way of explaining planetary orbits (kepler"s laws). And, in fact, he had worked backward from kepler"s laws to show that they were consistent with a force law like the one he worked out for gravity. What he needed to do was work out a specific example to test his idea. This led newton to ask the following question: Now, the moon is in a roughly circular orbit around the earth. This is because any change in velocity requires an acceleration. To change the direction that an object is moving requires a force, even if the object"s speed remain constant. Among the consequences of newton"s laws of motion are rules that govern objects in circular motion.
