1Physics 4810 / 7810 Week 5 - Learnin!Day 10: Fa2008:Knowledge in PiecesApplication to Newton, Dynamics and N3Jigsaw Approach(i) Form groups of disciplinary expertise(ii) Jigsaw / regroup into distributedexpertise in order to solve broaderproblemRedish Jigsaw1) What are our goals for physics instruction? 2) What is social learning? Does it include lecture? Doestechnology affect it? 3) How can we teach students "how to use multiplerepresentations and pick out the significant pieces ofinformation from a problem?" 4) How do these theories of memory apply to teaching andlearning? 5) What's better, bridging or cognitive conflict? What aretheir advantages/disadvantages? How would weimplement bridging in tutorials?Broad Question (from Redish)Broad Question 1: We've seen evidence thatTutorials are very effective at teachingphysics concepts. Why?b) Is it because they're "well-written"? Is itbecause they encourage social learning? Is itthe extra time spent?a) Should we scrap lectures and focus ontutorials? Is it too expensive? Will it just bethe "blind leading the blind", and thereforeproduce improper learning? What about un-social students?diSesssa Jigsaw1) Can you think of possible p-prims you have used orencountered? !Have you ever had your p-prims challenged byinstruction and learned as a result?""2) Is physics simply a way of reorganizing, clarifying, andexpressing p-prims?3) DiSessa notes a number of differences between p-prims andlogic. !Do you agree with his contrasts between the two? !Arep-prims not logical?""4) How does the second section of the paper (on dinosaurcartoons) relate to the first? !Why are these two sections inthe same chapter?""5) Has anyone experienced one of diSessa's "rare events" thatsparked your interest in physics in particular and science ingeneral? !Has anyone not experienced one of these events?If not, what got you interested in math and science?Broad Question (from diSessa)Broad Question 2: How do you makeuse of p-prims and rare events in theclassroom?2DiSessa• What is the relationship betweena p-prim and a conception? Isconception some sort of higher-level knowledge than a p-prim(i.e. is it made out of them?)? Iwould like to learn more aboutthese p-prims and look intoregorous studies on theirproperties and how we developthem.• Theme Music:David HildebrandThe MotionDetector Rag• Cartoon:Gary LarsonThe Far SideSeptember 10, 2001 September 10, 2001 Physics 121 Prof. E. F. Redish Physics 121 Prof. E. F. RedishDoing Science: Tools forBuilding Knowledge• Science is a process that studies the worldby:– Limiting the focus to a specific topic (makinga choice)– Observing (making a measurement)– Refining Intuitions (making sense)– Extending (seeking implications)– Demanding consistency (making it fit)– Community evaluation and critiqueMaking a choice• Chosing a chanel oncat television• Relates to thequestions we areaskingMaking a Measurement (and sense)• We think we see the world around us, but ...• How do we know we see things the same?(reliable)• How do we know that we see things correctly?(valid)• Our own VR:– We gather info through our senses– Our brains interpret these stimulae– But don’t necessarily get them rightMaking a measurement• Do these linesegments look thesame?• Are they?3Making Sense• What is this?• Hint: it’s an animal• Hint ][: it’s notoriented correctlyHmmmm….• Does this help?Making sense of physics• Does this look like dots• Or deep relations of electric forcesSeeking Implications• Elaboration -- when we assume one thing itis bound to have implications beyond theexact case we are considering.• Figuring out what something implies is agood way to examine the thing itself• And develop MODELS which areapplicable beyond our immediate caseSeeking consistency / Making a Fit• Science seeks consistency in patterns• Want our principles to be as broad aspossible• Breadth depends upon the state of what weknow• Physics has been around for quite sometime and hence, developed a high degree ofconsistency.4The puzzle analogy• Seek consistency• Patterns fit• Lack of consistencyleads to frustration• The same is true inphysicsNext steps… summary cues• Making a choice• Making a measurement• Making sense• Elaboration• Coherence• Theme Music: Indigo GirlsGalileo• Cartoon: Pat BradyRose is RoseSeptember 28, 2001 September 28, 2001 Physics 121 Prof. E. F. Redish Physics 121 Prof. E. F. RedishOutline• Recap of Free-Body Diagrams• Working out the implications• Newton’s 3rd Law• Reviewing Newton’s LawsExamplerNtable A!A B A rNhand A!rNB A!rftable A!B rftable B!rNA B!rWearth A!rNtable B!rWearth B!Implications!“If that’s true, then…”• Consider the example above.If we assume no friction,how does the pair of blocks speed up?• Consider them first as a single system.The problem is much simpler then.• Afterwards, lets consider it as two separateblocks. What does the result of treating it as asingle system tell us?5A+BrNtable A B! +rWearth A B! +rNhand A B! +m a NA B A B hand A B+ + ! +=rrNow consider each box separatelyA B BrNtable B!rWearth B!rNA B!ArNtable A!rWearth A!rNhand A!rNB A!ABAhandAANNam!!+=rrrBABBNam!=rrCompare the equations!• All the accelerations must be the same.( )( )m m a Nm a N Nm a Nm m a N N NA B hand AA hand A B AB A BA B hand A B A A B+ == +=+ = + +!! !!! ! !rrrr rrrrr r rA serious implication• In order for our treatment of the two objects as asystem and as separate parts to be the same wemust conclude:r rr rN NN NB A A BB A A B! !! !+ == "0orNewton’s 3rd Law• When two objects touch each other, eachexerts a force on the other.• Forces are interactions between objects.• In order for our analysis to be consistent,when two objects interact, the forces theyexert on each must be equal and opposite.• This must be tested experimentally.• Strangely enough, it works!ABBAFF!!"=rrDoes N3 always hold?• We were able to check N3 for a lot of casesof normal forces in tutorial last weekand it always worked.• Test it!• For tension and friction forces we could alsodo the experiment and see that it works.• For gravity (and electricity and magnetism)things are a bit more subtle.– We can’t really measure the effectof small objects pulling up on the earth(but they could be