## Day 89 – Projectiles

Physics 11 – One of the best things I have changed in physics is the order in which I do projectiles. From what I’ve seen across Vancouver, most teachers do projectiles at the end of kinematics. However, I now have students learn about them after we’ve done forces. At this point the students are about as good at drawing force diagrams and recognizing balanced forces as they will ever be. Therefore, the students in general have no problem understanding why a projectile only accelerates towards the Earth but not horizontally. They also have done some vector analysis with force diagrams, so the idea of vertical/horizontal components is not a new concept.

This is not to say that projectiles are easy for students. These questions often involve multiple small steps for solving and while the students can do each small step individually, putting them together into a complete solution is challenging. As well, this is a topic that only motivated students seem to do well in. I don’t have students hand in homework, so if they slack off, then the chances of them being successful is not that great.

## Day 88 – Forces Follow-Up

Science 8 – Following from last day’s lesson, today students formalized their ideas on forces by reading through the textbook and answering some questions.  The focus on this work was the differences between constant and non-contact forces, and what kind of motion results from unbalanced forces.

For the last 20 minutes of class, students were asked to put together a concept map for forces.  I gave them keywords such as: balanced, unbalanced, constant, contact, at-a-distance, gravity, electrostatic, etc…

Most of the class nailed the concept map – they had sufficiently complex connections that made sense (indicating they knew how the concepts were related) and the links and descriptors that were accurate and applicable.

## Day 87 – Exit Slip

Science 9 – Trying hard not to get mired in smaller details of reproduction, students did some practice with small concept maps of sexual reproduction and slide show overview of asexual vs sexual reproduction. The class ended with my asking for an Exit Slip. As many teachers know, this is a great formative assessment tool.

## Day 86 – Forces

Science 8 – Today’s lesson has students pushing a hover disk back and forth along a desk. While doing this, students are asked to make observations and try to answer the question, “what forces are acting on the soccer disk, and what is the result of force?”

There are a few key things at play in this activity. First, I ask students to identify forces acting on the disk. Kids will have a variety of ideas from 1 to 4 different forces. The two most common forces identified are the push and gravity. We then break it down a bit by looking at a stationary disk on the desk. From this, students are convinced that there must be a force pushing the disk up (otherwise gravity would pull it down to the ground). Eventually we get the point that maybe there are 3 forces acting on the disk.

Next, I put some restrictions on when we are looking at the forces – I deliberately set it up that we are looking at the forces while the disk is moving between two markers, and no one is touching the disk at this point. Students will say there is a push on the disk. The next question then is, if there is a push, who/what is doing the pushing? Obviously the kid, they’ll say. But wait, how can this be if the kid isn’t touching the disk? This causes some serious reflection from the kids. Eventually we get to the idea that there are only two forces acting on the disk (gravity and normal force), that these forces are balanced, and that it results in constant motion. Whew.

This can be one of my favorite lessons because it forces students to really think about where forces come from, and what it means to have balanced forces. It is also a good challenge for getting the students to make useful observations. However, there is a big downside to the lesson. With a class of 30 students, it can be very hard for every student to have a voice. In particular, students that aren’t as quick as others to catch on will not truly participate.

## Day 85 – Meiosis

Science 9 – The above picture is a snapshot of my reproduction unit plan.  As the science 9 classes worked their way through reproduction, I sort of got bogged down in details again.  I managed to avoid the small bits of meirosis and focused on how it results in genetic diversity. However, I don’t think the students had enough meaningful tasks by which they could really assimilate these new ideas. What I should have done is got them started on a transfer task or some intermediate project that focuses on the Understandings and Essential Questions.  Passively reading through some material isn’t much of a learning experience for them.  Next year?….?

## Day 84 – Drawing Conclusions

Science 9 – This is a result from one group’s experiment with yeast budding. Their experimental variable was water pH, and it looks like they may have made a mistake. This turns out to be excellent for everyone because it will give the class a chance to apply reasoning to an experimental results.

E: pH 3
F: pH 5
G: pH 7
H: pH 11

If maximum gas was at pH 7, then clearly the pH 3 solution should have less gas than the pH 5. It’s hard to tell from the picture but balloon E was the 2nd fullest.  A few students were able to apply CER (Claim, Evidence, Reasoning) to find this mistake.

## Day 83 – Universal Gravitation, oh my!

Physics 11 – Today was the kids introduction to calculating gravitational forces. It was supposed to be a pretty straight forward skill since the students already covered the concepts of gravity.  I even anticipated one problem from last year: students mistook the units for G as a formula.  So I mentioned this to the kids.

And then chaos ensued.  Basically it came down to how (un)comfortable students are with using symbolic representations.

Students can do this:   $10=\frac{160}{x^2}$    but they can’t do this:    $F_g=G\frac{m_1m_2}{r^2}$

They are fundamentally the same mathematical operation. For today, the one idea I gave students was to group the terms in their equation with a coefficient and variable. For example, when finding m2: $F_g = \left(\frac{Gm_1}{r^2}\right)m_2$

That helps to some extent but this is still confusing when finding r: $F_g = \left(Gm_1m2\right)\frac{1}{r^2}$
The solution to the above is to multiply both sides of the equation by the reciprocal of $Gm_1m_2$ and then take the inverse of $\frac{1}{r^2}$, at which point I might was well be speaking Latin.

Somewhere in mathematics education we need to really, really emphasize that mathematics isn’t just about numbers and that mathematical rules apply to all sorts of things. This is a huge cognitive gap with most students.

To finish things off, I had over a dozen students ask me what N and m stand for in the equation for G, and that they didn’t know what to do with the equation. So my question for readers of this blog: next year do I omit the units for G, or simply suffer through more questions about the “equation for G”?