-- recent post --
-Here's a question I ask all my students (regular and honors) about forces:
-A book rests on a table. If the book's weight is the action force, then
-the reaction force is the
-a) table pushing upon the book.
-b) book pushing down on the table.
-c) the Earth pulling down on the book.
-d) the book pulling up on the Earth.
-The majority of ALL student get this incorrect every year. More
-importantly, it generates an interesting discussion when we do it as peer
-instruction. It has made me rethink how I teach. You can do other
-variations of this question. It's a great way to challenge students'
-misconceptions.
-- end --
I've recently switched from action/reaction to interaction pairs. A switch in reference frame might change which is perceived as the action & which is the reaction. Action/reaction also tends to imply one of the objects 'caused' the phenomena to occur while the other was an innocent bystander. This is obviously not true.
If we discuss every such occurrence as an interaction, the 'fault' of the collision is gone. It is easier to see which objects are interacting (while easier, I'll admit it doesn't magically & completely remove the conceptual issue). It is also a bit smoother when discussing impulses. Stating that impulse-momentum methods work when we are interested in information just b4 or after an interaction is smoother than discussing action/reaction at that point. It also allows an easy transition & reinforcement with N3L discussions than if I subbed in action/reaction or collision etc...
To wonder is to begin to understand.
Paul Lulai
Physics Teacher
St. Anthony Village Senior High
Saint Anthony Village, MN
55418
(w) 612-706-1144
(fax) 612-706-1020
plulai@stanthony.k12.mn.us