Path: ...!weretis.net!feeder8.news.weretis.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Luigi Fortunati Newsgroups: sci.physics.research Subject: Newton e Hooke Date: Sun, 26 Jan 2025 08:51:04 PST Organization: A noiseless patient Spider Lines: 67 Approved: Jonathan Thornburg [remove -color to reply]" Reply-To: fortunati.luigi@gmail.com X-Trace: individual.net Ei0MjC1adBpS4z/btnyIAQfgoMvrytofPSJ9sjas0gXKakGWTjzu8ncWFt Cancel-Lock: sha1:Y2oJ5jm8/DrPk6Rh5AC1ZRFzcWY= sha256:1jYiu/Tr+gBoHtXNbuSEhaA5BhnwPsIB3SZoKAWGaHY= X-Forwarded-Encrypted: i=2; AJvYcCUYoIFVSh7ccAKZi09XS7V66bQcx1vD9p2GJZI3tZV7yZQd3T++Fin1tXgAHHd6p1jdGmR0IWMdYr923qgEgA==@gmail.com X-Auth-Sender: U2FsdGVkX1/rBT1bUgelept1yAH0oYZIKMjYyujW8ckvPHtJu4XNqYzXY8fCXGZP X-ICQ: 1931503972 Bytes: 4212 Newton's second law (F=ma) says that the greater the force applied to the mass , the greater the acceleration. It is quite obvious that this is the case: if a child pushes the car, the acceleration is minimal; if an adult pushes it, the acceleration is greater. Hooke's law says that the greater the force we apply to the body, the greater its contraction/elongation (tension). It is quite obvious that this is the case: if a child pushes a car, the tension at the point of contact is minimal; if an adult pushes it, the tension is greater. But then, how can we define force? Is it more correct to say that force is that thing that generates acceleration or is it better to say that it is that thing that generates tension? If force can generate acceleration and also tension, then it is more correct to say that force is responsible for acceleration and also tension. If we push a car with the handbrake on, our force causes only tension and no acceleration. If the handbrake is not on, our force generates tension and also acceleration. If instead of pushing a car we push a feather, our force causes (almost exclusively) acceleration without any tension. Therefore, both laws are natural, faultless and correct but they are also partial because one takes into account only acceleration neglecting tension and the other takes into account only tension neglecting acceleration. Is this reasoning correct or is there some flaw? Luigi Fortunati [[Mod. note -- Yes, there are multiple flaws in this reasoning: 1. In Newtonian mechanics, the concept of "force" is more general than *contact* force. For example, a magnet can exert a force on an iron object without every being in contact. 2. In Newtonian mechanics, a force applied to an object does not *necessarily* result in a contraction/elongation of that object. A contraction/elongation is the result of *differential* motion of different subparts of the object (presumably caused by varying values of F/m for different subparts of the object); if a force (such as a uniform Newtonian gravitational field) is applied to every part of the object such that F/m has the same value for every subpart, then there's no contraction/elongation of the object. 3. "Is it more correct to say that force is that thing that generates acceleration or is it better to say that it is that thing that generates tension?" Neither of those is quite right as an operational definition for force in Newtonian mechanics. You'd be better off with something like "*net* force is the thing that generates acceleration". There's a very clear, concise, and readable discussion of this in chapter 3 (particularly section 3.4, "Operational Definition of a Numerical Scale of Force") of Arnold B. Arons "A Guide to Introductory Physics Teaching" Wiley, 1990 ISBN 0-471-51341-5 4. Notably, the operational definition and the associated reasoning described by Arons do NOT make use of of Hooke's law in any way. Hooke's law is a separate logical construct, which may or may not hold for any given compressible object in any situation. -- jt]]