We finished WB’ing the Coulomb’s Law Practice problems. I really like this problem:
because it provides a chance to ask a few really nice follow-up questions. For example, (once the two forces are drawn in), sketch the net electrostatic force (a nice chance to quickly review adding vectors tip-to-tail). Another follow up is to ask for the position of the little charge +q (assuming A and B are anchored) an instant later…. then another instant later. The majority of students think the +q follows the net force line…. forgetting that now the two individual electrostatic forces are now different meaning another different net force. I think it provides a really nice preview for electric fields, where we are headed next.
We also discussed the Charge assessment they took yesterday.
We purple penned the work(ing) problems they solved in small groups yesterday. After this, we predicted one more graph from what we did yesterday… the Work(ing) as a function of time. You fully realize that it is linear:
and that the slope of this graph is the energy transferred each 1.0 second… or power. We wrote the EOL that, when rearranged, gives the usual power equation. We talked about the different units for power, watts ft.lbs/s and of course horse power. We even converted the slope for the student into horsepower… quite a few laughs about how small it is… the perfect segue into the activity called the Biggest Horse. This is just a simple activity that we use to have the students practice working, and power calculation by determining their power output. Here a clip of two students doing the simple activity:
It uses old 10 pound weights. I’d really love to find a set of 5 lb weights to give the students the chance to debate lower mass (force) in a shorter time or big mass and possibly slower time. We enter all the data into a spreadsheet to check the calculations and to rank the students. The Biggest Horses (make and female) in each class are given a prize… a Power Bar !!
For the last bunch of years (at least 10) one of our clubs (The Heart Group) has sponsored and planned a Diversity Fair. It is an impressive undertaking planned by this group of students to celebrate and promote our diversity. The fair officially kicks off with an assembly that sets the tone for the day. This year, the focal piece was a student created video about labels and being human. I am continually impressed with the work that some high schools students can produce. The rest of the day, classes still run, but so does the Diversity Fair complete with workshops and booths. Teachers can opt to take their entire class to the fair if they wish to. Because of the assembly, our classes were shortened to about 40 minutes.
We finished the Coulomb’s Law experiment but sharing the slope values for the final graph. The post lab discussion was this part was very easy because when the students wrote the EOL for the graph, Coulomb’s Law is what they write! After this, we looked at an easy sample problem. It took a bit to convince them NOT to put the sign on the charge into the equation. I explained that this sign is NOT a direction like our other (+) and (-). Any time left was spent working in smalls groups on a set of Coulomb’s Law practice problems.
Today was just spent completing the questions for the Racquetball leaper. Again a nice plan because it allows the students to ask for help as needed.
We just finished day one of the post lab discussion for the electrostatic force experiment (well, simulation). A bit more detail on how I set it up. Not only am I using this to build the model for Coulomb’s Law, Ia m also using it as a launching point for discussing the electric field. Here’s how. As we completed the pre-lab discussion, we agreed that when we looked at the relationship between the force and charge, we could only change the charge on on object, so we had to keep the charge on #1 constant as well as the distance separating the two. When I set it up I, assigned the constants such that we could look at the slope value for the electrostatic force as a function of charge would allow us to look at the characteristics of the Electric Field strength. Here is the handout ( Electrical Force Simulation(13-14) )and in the box, is how I used playing cards to set the constants and the field strength. Notice there are two groups that have the same distance but multiples of the charge, and groups that have the same charge, but multiples of the distance. This allows us to see how the slope (later to be defined as the electric field strength) is affected by the charge establishing the field, and by the distance away from the charge the test charge (q2 in this case) is placed. So here are the graphs:
This one provides a nice chance to discuss the difference between an inverse relationship and an inverse square relationship. For some kids, the first graph in this series in inverse.
So now we have three relationships: Fel proportional to q1; Fel proportional to q2; and Fel proportional to inverse square of distance (1/d^2). We want all three in one Fel proportional to q1q2/d^2 and we want an equation for the electric force. So to change the proportional to an equal sign, we need the proportionality constant (or slope) of that graph Fel vs q1q2/d^2. Here is it:
I think you recognize the slope!
Some of you may already know about the BigBlueButton Conference app. It is hosted in Schoology which the incredibly awesome LMS our district has bought into. The BigBlueButton app allows you to video conference with your students. You can also limit it to just audio or mute the mic and go all typing. It allows you to upload a pdf and the annotate as your heart desires. It even allows the session to be recorded. I just used it for the last two night with my CAPP kids that were working on a rather challenging set of momentum-impulse problems that are due tomorrow. It is really sweet watching/listening as the students ask questions and answer each others. Talk about fostering collaboration and communication… those of us that are required to complete the Educator Effectiveness Project are all set.