Unit 4 - Free Particle Model - Inertia and Interactions

First of all, we brainstormed about what a force actually is.  What comes to mind when you state the word "force?"  We were led to understand the 1st rule of forces which is that "All forces must be caused by a physical object made of matter" and then to realize that a force is a push or pull caused by a physical object made of matter.  We looked at something simple as a hand holding a book and developed a schema which is a tool to help draw a force diagram.  All objects involved with the object are included in the schema and then ultimately we only look at the interactions between objects (We decided to ignore air for now because it has little effect on the book right now, we may include it later.)  Here is an example of a schema and its corresponding force diagram.

At this point, we also looked at force diagrams and talked about "shadow vectors" based upon shining light onto the vector from on top or from the side and we would get different sized vectors.

We looked at how the table could be exerting a force onto the bowling ball.  We looked at a spring and a person holding a book and how they always sprung back after the weight of the book was added.  We also looked at magnets with holes on a rod and how they repelled each other.  We related that to the electrons in atoms on the table how they repel.  Another way to convince students that there is a force exerted from the table is to reflect a laser beam from a pointer onto a mirror onto the ceiling and the press on the table and it adjusts a little.

We also established that if there is no change in velocity, then the forces are balanced.  We also looked at the non-contact forces and established that contact forces would be everything else.  We then did some worksheet problems and whiteboarded them.  We also had a good discussion about what constitutes a Newton's 3rd Law force pair.   We setup a lab where we connected force sensors onto two different carts and did a number of tests on them.  Here is a picture of one possible setup:

Other setups included where one car was moving and other over took the first one; connected springs between them; among other scenarios.  All showed equal and opposite forces.

Basically, the force units melded into each other, so I am not really sure where one ended and the other one began :)

I will continue on with the next unit as a continuation of forces by discussing Newtons Second Law