College-Prep Physics: I didn’t anticipate spending a whole period about how a fan cart works. Nor was I expecting students to say a fan cart’s speed would accelerate up to a constant speed.
Transfer is hard. We had already done the bowling ball and mallet activity. But this wasn’t a bowling ball. It was a fan cart. In their minds, different objects means different outcomes.
That’s when I came up with the idea of “physics goggles.” When you’re wearing your physics goggles, you see past the superficial features of different situations and focus on the underlying principles. In the case of the fan cart, the air molecules were providing the “taps” to accelerate the cart. And since those “taps” never stop, the cart would continually increase speed, just like a tapped bowling ball.
While students agreed that you could get the bowling ball to go as fast as a Ferrari (even with tiny taps, as long as you could keep up with the ball), they initially struggled with the fan cart going as fast as a Ferrari. Most thought the top speed of the fan cart was determined by the speed of the fan.
“Time to put on our physics goggles!”
Student A: “The forces are ALWAYS EQUAL. That’s what we’ve been talking about for the past week.”
Student B: “Well, if B is at rest, then the two forces must be equal.”
Student C: “The force from C must be greater since it bears more weight.”
Student B: “But if the force from C is greater, then B would move upwards.”
We’re in a difficult spot right now, and I probably should have delayed this question until after we talked about gravitational forces in more detail. But, it was on the HW sheet for a Preconception in Mechanics lesson that we already did, so I just photocopied the worksheet without really looking at it first. *hangs head in shame*
We were able to get to a point where:
- We understand that the force from C must be greater because the surfaces between B & C deforms more than the surfaces between A & B, since surface C is supporting the weight of both block.
- We don’t understand why block B remains at rest, since the 2 forces on B are different in size.
My best answer to them was to put a big question mark on it and return to it later. We don’t have all the pieces to this puzzle yet. Students didn’t really like that answer and left class a bit frustrated.
I really resisted doing an impromptu gravitational force lesson, since I’m saving it for later because that’s how Preconceptions in Mechanics does it. I think the reason they delay gravitational forces and do normal forces first is because kids often confuse the two forces when objects are resting on top of each other. For example, using the problem above, many kids think that the gravitational force on A literally is the normal force of A pushing down on B. In this case, they have the same magnitude, but they are really two distinct forces.
Conceptual Physics: This student is literally watching paint dry. He’s looking to see if more watered-down watercolors take longer to dry. The columns represent the number of drops of water added to the base paint (3, 6, 9, 12 drops). The rows represent the 3 different trials he’s performing for each. The numbers to left of each square is the drying time.
College-Prep and Conceptual Physics: Students will be reporting the results of their self-designed lab experiments in the form of a scientific poster. I made this mock-up during my prep periods today. It’s based on Colin Purrington’s design, but scaled down to fit standard 22″x28″ posterboard that you can buy at your favorite office supply store. Of course, students are free to use the poster as they see fit, but I split the poster area into 8 sections for easy planning, printing, and pasting. The Word template has the appropriate margins and prints with a dotted line around the margins for easy cutting: PosterTemplate22x28.
Also, I had two great conversations with a few students today about their projects. In short, I don’t want them to just document the end result. I also want them to tell me about any trouble/glitches that arose in their original design and what/how/why they modified it. For example, the student who was watching watercolors dry wasn’t noticing any difference between adding 1 drop, 2 drops, 3 drops, and 4 drops of water to the base paint. We decided that perhaps a delta of 1 drop wasn’t enough to make a difference. Maybe 5? He’ll try again on Monday. — > That is what I really value. The thinking and creativity behind experimental design. I want their posters to reflect that, rather than look like they knew exactly what to do and followed it perfectly and got flawless data.
Conceptual Physics: Our bike light generator unit is done, and we have 7 days of school left. Definitely not enough time to begin the last unit from “Physics That Works.” So students will be designing their own lab investigation instead. This will be similar to the College-Prep projects, but with some more structure and scaffolding.
I recently read an article about Inquiry Boards in Science and Children (NSTA’s magazine for elementary teachers). It provided a perfect structure for helping students focus on variables in science experiments. I took the basic structure of the Inquiry Board process and rolled it into a proposal sheet: Lab Experiment Project Proposals. We walked through the example about plant growth, highlighting the difference between variables we could change and variables that we can change AND measure. For example, you can change the amount of light the plants would get, but we couldn’t quantify the amount of light (at least with tools at hand).
The student whose proposal is pictured will literally be watching paint dry! You can see how it progressively gets narrower in our focus. First from many variables and outcomes, then to the measurable variables and outcomes, then to picking just one measurable variable and one measurable outcome, and therefore the controls must be all the variables we didn’t pick.
- A generator-battery circuit that recharges the battery while pedaling.
- A generator-bulb circuit that lights the headlight and taillight while pedaling.
- A battery-bulb circuit that lights the headlight and taillight when not pedaling.
College-Prep Physics: Double slit with laser pointer demo to begin wave model of light. Knowing how light behaves will help use decode the light we observe from stars and galaxies. Used this slide that has multiple slits and gratings on it:
It’s really old. Here’s what it says at the top (click to embiggen):
Also showed this AWESOME movie of interference in a pond:
AP Physics C: Today was the AP exam. One student showed up to class this morning, even though the exam didn’t start until noon.
Conceptual Physics: We played a review game using clickers from Eduware. We chose Eduware clickers because they have test banks of old Regents Exam questions and come with several different games (Jeopardy, Racing, and Tug-of-War). That’s really the only good things about the system. Using it as a traditional clicker system with Powerpoint is awkward, as is generating questions on the fly. Even though our school dropped the giving the Regents Exam in physics, I still use the software and clickers from time to time.
College-Prep Physics: Students determined the relationship between angular size and size/distance ratio. Handout: A Handy Measuring Tool Part 2 Angular Size
AP Physics C: Mechanics multiple choice review.
Conceptual Physics: Students attempted to figure out the wiring inside 8 different mystery circuit boxes by unscrewing the 4 light bulbs for each box. (Well, really 7 because one box needs repair.) I built them a number of years ago with a lot of help from my dad. If you’re not very handy, you can rewire bar light fixtures purchased from a hardware or lighting store. (See: Mystery Circuit Box and Make a Mystery Circuit with a Bar Light Fixture.) I used 15-watt bulbs that have a standard base (clear glass whenever possible). They are a bit more expensive, but they never get too hot to touch. Students enjoyed solving these circuit puzzles!
College-Prep Physics: After graphing the data from yesterday’s activity, we saw that when objects have the same apparent size, they also have the same size/distance ratio. We used this concept to create a “handy tool” for determine the size or distance to unknown objects. Students were challenged to determine the distance to the doors at the end of the hallway and to determine the height of the flagpole. In the picture above, the width of my pinky finger held at arms length is the same apparent size as the height of the doorway at the end of the hall. How far away is the doorway? What assumptions are you making? Handout: A Handy Measuring Tool 2013
AP Physics C: No class. All students were taking the AP Calculus exam today.