Lecture 02:Interactions And Systems Lecture Created By: Andrew N. SumerelBased On Conceptual Physics 12thEdition By:Chapter 5: NEWTON’S THIRD LAW OF MOTIONPHY 110: Conceptual Physics
•How is Newton’s Law Of Motion considered for multiple objects?–What can objects do to eachother?•How are interactions quantified?•Can interactions describe motion?•To what situations do these considerations apply?–Are there relevant and familiar examples?Interesting Questions To Answer In This Lecture2
•Forces And Interactions•Interactions And Motion•SystemsRelevant Topics For Answers3
Forces exist when one object does something to another object.So an interaction requires a pair of forces acting on two different objects.Example:•interaction of hand and wall–involves a force pair•You push on the wall.•The wall pushes on you.•interaction of truck and train−How does the train’s force compare to the truck’s force?Term DefinitionForces And Interactions4Click MeDuringSlideshow!
Newton’s Law Of Interaction(Traditionally Newton’s Third Law)Whenever one object exerts a specific force on a second object, the second object exerts a force on the first that:•is the same kind of specific force,•is equal in magnitude but•is opposite in direction.•In equation form:Physical RelationshipForces And Interactions51on22on1FF
Force pairs during an interaction•are co-acting.–Neither force exists without the other.•always act on different objects.•are always the same kind of force.•are equal in strength but opposite in direction.These nontrivial notions are missing from the common, alternate form of this law:For every action there is an equal but opposite reaction.Procedural RemarksForces And Interactions6
Examples•The push here is really the force of friction•For these examples, we may feel confident in defining an action and a reaction, but in most situations this characterization is impossible.−The Law Of Interaction does prefer one force over another so ignore the idea of action/reaction.Forces And Interactions7