Teacher notes for IPS Force unit

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Students should understand that a force moves a mass (object) by accelerating it. Students need to be familiar with velocity (displacement as a function of time) and mass.

Class 1 (Day 21, on the unit plan): We started with the PhET force simulation and this handout. It took about 30-40 minutes and students were able to discuss and demonstrate balanced and unbalanced forces, using examples. (All did well on a short quiz the next class, so I inferred that this sim was helpful.) Students needed to be reminded to write both the magnitude and direction of the force in the box on the far right of their table on the handout. They wanted to write "X-left" instead of "50 N left" for example. Finally, we defined force as "a push or pull" and sketched basic force diagrams, using applied, normal, gravitational, and frictional forces. We looked only at forces moving paralell to the Earth's surface. We added terms to their terms list in their binders: force, balanced force, unbalanced force, force diagram, net force, inertia, and normal force, applied force, and frictional force, so that students could apply and make sense of their understanding of balanced and unbalanced force. We only looked at force diagrams force diagrams in one plane, so no trigonometry is needed. Students already had an understanding of friction and brought it up several times, so we added it to our force diagrams to show that the force of friction works in a direction opposite to the applied force.

Class 2 (Day 23 on the unit plan): View and discuss a 7 minute video from Bozeman Science. We watched the video once without notetaking or discussion. At the end, we talked a bit as a class about what they remembered about Newton and each law, using this handouthandout page 1 ( in Cornell notes format, sort of) and then watched again, stopping to talk and write about what was important. We used handout page 2 as a graphic organizer to summarize Newton's 3 laws.

Inertia is always confusing. We defined inertia as the tendency of an object to resist a change in its motion (or stillness.) A simple inertia demo was pulling a sheet of printer paper out from beneath a large can filled with pencils that sits on the corner of the front table.

We then looked at a modified Atwood's Machine as a demo. Links to basic info are at the bottom of this page. I made a crude setup by tying thick string around a large book and leaving a tail of about 2.5 meters. I tied the end to a 1-kg hooked mass and suspended the mass over a pulley at the end of my front lab table.I placed the book on the table as far from the pulley as the string allowed while the mass hung at the end of the string over the pulley. Adjust the string to that the book is stopped by the pulley clamp just before the mass hits the floor.

We drew a force diagram for the Atwood's machine model.

I'd originally planned to let the students make and mess with their own machines, but our pulley clips don't fit the edges of the table. Tuns out I could have, since the setup I used worked nearly as well without a pulley.

Then we had a quiz over balanced and unbalanced forces and a simple force diagram, with applied force, and frictional force as unbalanced forces and force of gravity, and normal force as balanced forces. Students did very well.

Class 3 (Day 25 on the unit plan): We just had a week off for Thanksgiving break, so we will take a new look at force in preparation for starting energy, with a focus on the importance of our work so far.

 

Links to simple modified Atwood's machines (We don't need to collect data for this work. The motion sensor worked well though, if I placed a paper tent atop the book to catch the signal.)