Beach Slope and Grain Size

This week has involved a different type of school! I’ve worked with another physics teacher to plan activities related to “Waterways and Wetlands” in New York City. Today, in about 15 degree weather, we went to the beach!!

To compare the beach at Jacob Riis Park to the others around the country, we first measured the slope of the beach at a few different places. The average value was about 1:20 meaning the for each one centimeter of vertical change, there’s a horizontal change of 20cm.

We collected sand samples, took them back to our school and dried them out.

The we used sieves to figure out what the most common sand size was. Most of our sand was between 0.25mm and 0.5mm wide. We could actually use a more complex algorithm to determine the mean sand width, but that would have been over the heads of our group. (It turns out to be about 0.4mm.)

This combination of about 3-4 mm sand and a 1:20 slope is very typical for a beach that’s exposed directly to the waves. Google image search “grain size slope” to see the relationship for many other beaches.

##pbl

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First Day of Spring at Rutgers! (Flashing LED at 60Hz)

In the evening after school, I had my first class of “Multiple Representation in Physical Science”, my last official class in the sequence with Eugenia. We did experiments with LEDs, comparing the activation potential for both red and green.

Somewhere along the line, we had the idea to test the idea that an LED would flash at 60 Hz if hooked up to an AC supply. But how can you see flashing at 60 Hz with your naked eye? Easy! Just wave the LED back and forth and look for the breaks in the stream of light!

In fact, with a little cleverness, you can tell a lot from this photo. About how fast is Eugenia’s friend and colleague’s hand waving? What’s the shutter speed on my camera?

##electricity ##testingexperiment ##isle

Waterways: Red Hook

An usual day today! My school has chosen to do away with midterms and offer students a two week long experiential curriculum, designed by various teachers. The three days that I was a part of planning are about waterways and wetlands in New York City.

Our first day was about trying to get a feel for what “Superstorm Sandy” really meant for a lot of residents of Red Hook. We visited the “Waterfront Museum”, which is built on an old train barge.

Amazingly, the barge simply floated up and then back down, following the storm surge up to about 12 feet above today’s low tide! You can see the high water mark in orange, painted on the metal piling.

Of course, most Red Hook residents weren’t so lucky to live in a floating home. This map of the neighborhood shows the parts of Red Hook that were flooded.

Tomorrow it’s off to the Gowanus Canal for some history and water testing!!

##pbl

Dueling Whiteboards

A colleague of mine came up with an awesome take on whiteboarding that lives in the space between whiteboard making and whiteboard presenting. Finding the sweet spot in this regard is sometimes tough, since whole class discussions of whiteboards can often either a) encourage some students to keep quiet, assuming that others are going to keep the conversation going, or b) take too long to get to every board that was made. This technique takes on both, and it worked really nicely for me today when I tried it for the first time.

The idea is simple… Make an even number of whiteboarding groups, and assign each of them one of two problems. Give them a bit of time for whiteboarding (with ##mistakes if possible!), then pair up the groups. Instead of presenting to the whole class, they’ll just present to the other group. Then, after all mistakes have been cleared, the other group presents.

In the past, I’ve also had some success with whiteboarding one problem on multiple boards around the room, but this can feel a little stagnant, and we only see one problem! This “dueling whiteboards” technique is much more dynamic, and more effectively convinces everyone in both groups that their participation and careful thinking is absolutely necessary!

##whiteboarding ##physicsfirst

Buggy Collision Calculations

Got around to the buggy collision a couple days ago. Students were successful, and it’s a pretty awesome check for where they are in the course, both conceptually and algebraically.

I thought it was interesting that many, many groups wanted to measure the velocity of the buggy by dropping salt packets and making position vs time graphs. On the one hand, this is BEAUTIFUL, because they’ve internalized the definition of velocity. On the other hand, since confirming *constant* velocity isn’t really our goal, dropping the packets is superfluous, and I’d expect them to see that measuring on displacement and average velocity is plenty.

I know this gets at a question of priorities – what we’re actually teaching here, but I’m not totally sure how. Any ideas?

##cvpm ##practicumlab ##setbacks

Ruling the Mistake Game!

I haven’t done the mistake game much this year, but today makes me think I need to be doing it every whiteboarding!! The mistakes on these constant velocity boards were just too awesome!

This group did the classic “xi – xf” mistake, drew a graph that got steeper not shallower when the velocity decreased, AND left units off of their calculations! (That last one was involuntary, I suspect, but that’s the great thing about the mistake game!)

This group took the prize, though. They chose to calculate an average velocity over the entire time interval, rather than just the first four seconds where the velocity was constant. This got us into an awesome conversation about the difference between average velocities for different time intervals, which is a crucial distinction that otherwise wouldn’t have come up.

##mistakes ##whiteboarding ##cvpm ##representations

Waves on Slinkies and Simulations

Getting into waves with the AP class, and I’ve introduced the topic with a set of questions that require brief experiments to solve.

One thing I’m excited about is the combination of real-life slinkies and the PhET “Waves on Strings” simulation. I told students ahead of time that some questions can be answered much more easily using either the simulation or the real equipment. Some of them can be observed in both, and different details will emerge from these different perspectives.

“A periodic disturbance on a slinky/string held both ends such that every point on the slinky is undergoing simple harmonic oscillation simultaneously” is most easily observed on a slinky.

“A periodic disturbance moving continuously in the same direction through a medium such that every point on the slinky/string is undergoing simple harmonic motion” is most easily observed in the simulation (where “reflection” can be disabled).

##waves ##ap ##simulations ##tech ##phet