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Day 153: Frequency, Wavelength, and Toy Buggies

College-Prep Physics: Used the long slinky to generate discussion about how we might make the waves travel faster down the slinky. That lead into a dissucssion about frequency, wavelength, wave source, and wave medium. Then students used constant speed buggies, adding machine tape, markers, rulers, and a metronome app on their phones to experimentally determine the relationship between frequency and wavelength. (Sorry, I’m reposting the video from last year.) Also showed this I Love Lucy clip:

Conceptual Physics: Students finished building and testing their modified bike light circuits and began making their final annotated circuit diagrams.

AP Physics C: All but one student was taking the AP Macroeconomics exam today. We’ll finish reading Arcadia tomorrow.

Day 152: Interference of Light

College-Prep Physics: Tied our observations of yesterday’s slinky wave interference to water wave interference and then to light interference. Showed this totally awesome Veritasium video about Young’s original double slit experiment (done with sunlight).

AP Physics C: Continued reading Stoppard’s Arcadia. In the video, Stoppard reads 2 of my favorite scenes from the play.

Conceptual Physics: Students finished building and testing their modified bike light circuits.

Day 149: Angular Size


College-Prep Physics: Looking at the graphs from yesterday’s activity relating angular size to size/distance ration, we saw that it’s a proportional relationship, though the slopes varied between 50 and 80. Much of the variation had to do with estimations, eye-balling, and compounding errors. So we derived the relationship using circle geometry:


Then we put the relation to use, determining the angular sizes of the sun and moon during an annular eclipse, the size of the Earth as seen from the moon, and the size and distances of nebulas and galaxies. Handout: Angular Size Homework 2013 (adapted in part from this).

Conceptual Physics: Chapter 14 quiz on series and parallel circuits. Bike light projects to start next week.

AP Physics C: E&M multiple choice practice questions. Monday is the AP exam! #fingerscrossed

Day 146: Size, Distance, and Eclipses


College-Prep Physics: How can the moon eclipse the sun when the moon is so much smaller? Students investigated the relationship between size and distance for different objects when they have the same apparent size. Some chose to eye-ball it. Others decided to use their phones. Handout is here: Size Distance Ratio LAB 2013

I tried it myself last night:

IMAG2143-1 IMAG2145-1

Conceptual Physics: “Predict and Test” exploration for series and parallel circuits. Handout: SeriesParallelPredictions Post Job 14-2

AP Physics C: Inductors in circuits, sample AP problems.

Day 145: How Does the Sun Rotate?


College-Prep Physics: Today we used the data from our sunspot log to determine how fast the sun rotates. Do the sunspots speed up, slow down, or move at constant speed? Do all places on the sun rotate at the same rate or does it depend on latitude? The lab handout is here: LAB Solar Rotation 2013

Conceptual Physics: Students used the PhET circuit simulation to explore how current and voltage behave differently in series and parallel circuits.

AP Physics CPractice AP free response questions on Faraday’s Law.

Day 141: How Big is the Sun?


College-Prep Physics: It was sunny out today! So we poked a hole in the side of a copy paper box to make a pinhole camera. Aimed our cameras at the sun and measured the resulting image in order to determine the true size of the sun. The copy paper box worked beautifully: the sides with the hole and the screen are always parallel; it’s easy to aim the camera directly at the sun — lay box on ground and lift up/turn until box shadow is square; for the size of the box, the image of the sun is exactly 1/2 cm across (so it fits perfectly within 1/2 cm graph paper). We didn’t do anything fancy with foil like I’ve seen for other pinhole cameras on the internet. Should we have? Why?


Conceptual Physics: Students finished the diode circuit simulation activity from yesterday. One group came up with a possible bike generator circuit that will charge the battery and light the bulb while pedaling, and will also use the battery to light the bulb when the pedaling stops.

Day 140: Gravitational Force vs. Distance

College-Prep Physics: We were supposed to go out and explore pinhole cameras, but it was cloudy. So today we explored gravitational force with a sim from The Physics Classroom: Students are doing a similar analysis like they did with light intensity a few days ago. Handout here: ACTIVITY Universal Gravitation 2013

Conceptual Physics: I found a great circuit simulation which has diodes (PhET doesn’t have diodes): Students explored diodes and AC circuits with this today. Hopefully it will allow them to understand diodes better and be able to come up with a draft of their modified bike light generator circuit. Handout here: DiodeCircuitSimLab2013

Day 139: How Bright is the Sun?


College-Prep Physics: A wax photometer (two parafin blocks taped together with foil in between) is a neat little device which can show you the relative light intensity of two light sources. When the light intensity is equal on both sides of the photometer, the wax blocks are illuminated equally:


When one of the lights is moved twice as far away, the wax blocks are of unequal brightness:

IMAG2052 (1)How many light bulbs would need to be added to the left side so the light intensity on both sides of the block would be equal again? Based on yesterday’s investigation, we saw that when distance changes by factor n, the light intensity changes by factor 1/n2. So, in this case, we’d need four bulbs on the left side:

IMAG2051 (1)What was amazing was that a student then asked, “Could we do this comparison with the sun?” … which is exactly what I had planned 🙂 . Groups of students took turns going outside and repeating the experiment with the wax phototometer and a 200 watt bulb in order to calculate how many 200 watt lightbulbs would be as bright as the sun (first picture).

Conceptual Physics: Students began drafting possible circuit designs to modify the bike light generator so that: 1) a battery lights the bulb when the rider is not pedaling and 2) that battery gets recharged while the rider is pedaling.

Day 138: Light Intensity vs. Distance

College-Prep Physics: Students designed a lab to determine the relationship between light intensity and distance. But first in the pre-lab, they made observations about moving the light, the square hole, and the grid paper. Then they had to invent a “light intensity factor” much like they had to invent the “cheesiness index” the other day. Finally, we agreed upon a common factor for us to all use in the lab: light intensity = # light bulbs / light area. This was similar to cheesiness = # bags of cheese / pizza area. The handout is here. The graph and analysis they had to do was identical to the math relationships we analyzed yesterday.

Conceptual Physics: Students used the bike generators and a diode to charge a rechargable NiCd battery. They pedaled for 20 minutes, stopping to take a battery voltage reading every 5 minutes.

Day 136: The Cheesiness Index



College-Prep Physics: We did the following invention task in preparation for understanding light intensity.

You work in a pizzeria. The pizza cheese comes in pre-portioned bags. Below are the recipes for making different pizzas:

  • 12″ round – 1 bag of cheese
  • 14″ round – 2 bags of cheese
  • 16″ round – 3 bags of cheese
  • 12″ x 12″ rectangular – 1 bag of cheese
  • 12″ x 16″ rectangular – 2 bags of cheese
  • 12″ x 20″ rectangular – 3 bags of cheese

Rank the pizzas from most cheesy to least cheesy. Explain your reasoning.

Invent a way to calculate the “cheesy-ness index” of any pizza.

You can read more about Invention Tasks and Preparation for Future Learning here.



Conceptual Physics: Used PhET circuits simulation to explain how to to interpret current and voltage vs. time graphs for AC circuits. Drew snapshots of how the electrons were moving (speed, direction) at different points in time. Used a bi-color LED plugged into the wall outlet to show household circuits are AC. When the LED is at rest, it looks orange. When you twirl it, you can see it actually the LED alternates between red and green, depending on which direction the current is flowing. Ended with closer look at PhET Faraday simulation to see connection between how the magnet moves (toward/away, N-pole/S-pole) and the direction of the induced current.