Wednesday, June 24, 2015

Speed of sound

Michael Yarofaitoar on the clapping blocks

Measuring the speed of sound deployed the approach taken last spring. The weather cooperated, clouds kept the sun from being too hot, yet rain did not fall. A couple future notes. The key to seeing the clap is start with arms at ninety degrees, boards angled to catch the light from the sky, flat face forward towards timers. The middle of the road is best, less visual background clutter. The clapper should be informed that cars behind them are a "no go" condition as the timers cannot always see the boards against the backdrop of cars. The timers need the pavement and fall hill as a backdrop. The clapper can and should get out of the road when traffic is present. The timers will understand what is happening. The clapper was up near the cement box for the power line to the well, slightly east of the crest used in prior terms. This worked better than I had hoped. I suspect the clapper could be even farther east, but intersection traffic would be a problem.


 This term I decided to use the surveyor's wheel in lieu of a GPS and this was a good choice. The wheel is more accurate. I did have to run conversions on the fly. 500 feet was too fast, too close. The first time was at 750 feet. After that we moved out 250 feet at a time. Julie-Ann rolled the wheel, others timed or recorded data.


 My calculator is on walk-about, so I used my cell phone to convert feet to meters using ×  12 × 2.54 ÷ 100.  The clapper is quite visible to the naked eye despite the distance.

Rofino timing. 

Julie-Ann Ardos on teh wheel

Surveyor's wheel at 1250 feet (381 meters)

Edward used the towel to flag the clapper. A larger, brighter towel might be better. Julie-Ann on the left, Rofino, Edward, Jayann, Barry, Alwin.


Julie-Ann, Edward, Pelma Dilipy, Alwin Alik, Sharon Mualia

Cherish, photographer.

Wrap up was at a picnic table.


The results were better than any echo synchronization version of this laboratory. Note that the median was used for the times gathered to eliminate the effect of outliers. In the field obviously wrong times (3.32 seconds or 0.52 at 533.4 meters) were not recorded. Even with obvious outliers discarded as timing errors, there will still be "reasonable" outliers that the median is insensitive to. 

I remain surprised that one can see the clapper at 600 meters and that one can hear the clap at those distances. The taking of extra data at 533.4 and 609.6 is particularly useful as the linear regression is more "sensitive" to end values. Getting the 609.6 data point correct is critical to reducing error. 

The approach of starting short and going long is also exactly right: the timers improve with practice and are most on top of their game when they reach at 600 meter distance. This also gives the group some short range practice where seeing and hearing are fairly easy.

Weather station visit

On Tuesday the physical science class visited the National Weather Service, Pohnpei Weather Service Office as a part of a unit on weather.
Edward, Cherish, and Rofino observe as Wallace explains some of the data displays

The class listens intently

Wallace holds the LMS-6 Radiosonde

The radiosonde unit

Theoretic tsunami arrival times from an earthquake in the south Pacific

IR color enhanced satellite photo of western Pacific ocean

Radiosonde data display

Balloon away, released by Eiko


Eiko Ioanis, on the left, was allowed to release the balloon. Perdania Barry, and Alwin look on

Back inside Sharon Mualia, Edward, Perdania, and Rofino watch the radiosonde data display

Radiosonde data

Chatty Beetle for communicating data as text messages among the outer islands. Satellite based, the messages are received across the Pacific.

A future meteorologist, perhaps, at her workstation.

RipStik sine wave trigonometry

I introduced chapter six, section four of the Larson Alg & Trig text with twin RipStik runs at two different frequencies. Neither run was timed, I opted to focus on wavelength rather than period and frequency to introduce wave concepts.


I opted to use three sheets of paper end-to-end.


 I then made a low speed pass north side pass, unstable but with the hope for a higher frequency.


My second pass was on the south side at speed but I did not well hold my line of travel. I have learned in the past that moving the paper east helps, but a class was in session in A203, so I did not want to risk disturbing that class.


Hard to see, but the north pass was amplitude 3.5 cm with a wavelength around 42 cm, highly variable however. The south pass came in at about an 80 cm wavelength, also 3.5 cm amplitude.

Sunday, June 21, 2015

Pi on a clothesline near the equator

In MS 101 Algebra and Trigonometry I opened the chapter on angles and radians by introducing a dimensionless measure of angles out on the lawn. I put Seagal at the center and then had Tammy walk the surveyor's wheel around Seagal at the end of a 44 foot long piece of clothesline. I probably should have given the line to someone else to keep the line taut as this would prove problematic out between pi over two and pi radians. Every ninety degrees I took a measurement and placed a student. Hansha was at zero next to the A building generator. Moving counter-clockwise, Patricia was a quarter turn, Maggie opposite Hansha, and Shellany at three-quarters of the circle.

Circle complete, Seagal on center, Natasha and Hansha at zero, Tammy holding the wheel, Patricia up at pi over two. Note that Natasha now has the line.

With Hansha at zero, Patricia was 68 feet worth of arc length away. Divided by 44 yielded the dimensionless 1.55 radians. Maggie was at 145 feet around the circle, 3.30 radians. Shellany 216 feet, 4.91 radians. The full circle was 295 feet, 6.70 dimensionless radians. 

Natasha with the line

There is more line, but not enough space on the front line to use the full line. Moving north would not help significantly: the hill to the east is problematic, the terminalia to the north is also limiting. Still, the concept can be well demonstrated that angles need not have units if they are specified as arc length divided by radius.

A Google pan of the three shots stitched together with some artifacts.


Meters per minute of longitude

In the morning the class worked on finding Binky. This term Binky was at North 6° 54.570', East 158° 09.337'. Binky was hidden in the tall grass at the bottom of a tree down a slope off the edge of campus. This led naturally to the question of just how close to Binky could the coordinates have put a searcher? Put another way, how far is 0.001 arc minutes in meters?

Laboratory seven sought to determine the conversion factor between meters and minutes. The conversion factor would allow one to convert 0.001 arc minutes to meters.

Julie-Ann Ardos with the surveyor's wheel

Spring 2015 I sought to decrease the error by using a more precise conversion between feet (measured by the surveyor's wheel) and meters. Rather than use 100 clicks on the non-metric surveyor's wheel as 30 meters, spring 2015 I went ahead and converted each 30 meter interval into feet: 98, 197, 295, 394, 492, and 591 feet. I then rolled the wheel while holding a crib sheet with the equivalents in feet.

Barry Diopulos watches the latitude in the rain

This summer I decided to run with the original 100 click design which is known to have about 1.5% error out at 600 feet. The 100 click rule (100 feet) allowed a student to take over the surveyor's wheel work.

Julie-Ann, wet but undeterred

The class started at 158° 09.600' east which made for easier subtraction of the start longitude. Visually the change in arc minutes is also easier to comprehend. 158° 09.000' would be better yet, but that is not on campus. This term a start at the "second palm" put the latitude at 6° 54.570'

Joemar Wasan, Barry, and Sharon Mualia watch their GPS units. Rain is falling harder, but they are undistracted



The rain chased away all but five students by the time we reached 600 feet (roughly 180 meters): Julie-Ann, Pelma Dilipy, Joemar, and Barry.


Sharon shows Pelma and Julie-ann her GPS readings


Barry and Joemar at 600 feet


The results of the data are close to the published value of about 1842 meters per minute. The slope is within 3% of the true value. 



On Friday the class took the midterm. Binky was there at the midterm.

Finding Binky

During the summer term I introduce latitude and longitude through a discovery learning exercise. I give the students a set of coordinates and a GPS. Other than turning on the GPS and paging to where the latitude and longitude is displayed, I give them no other directions other than "Find Binky!" I do let themknow that when the numbers on the GPS match the Binky numbers, then they should be where Binky is.

Binky, summer 2015

At the Binky hide, 6:27 in the morning

Binky's tree on the right down a slope of Ischaemum polystachyum (paddle grass, reh padil)


Initially there is only confusion, pairs with GPS units walking in random directions trying to see what happens to the numbers on the GPS.

Rofino Roby and Franzy Hetiback study the changing digits

Sharon Mualia comparing the numbers on GPS with those on the paper

Michael Yarofaitoar also comparing the values as he walks in the general direction of Binky

Joemar Wasan with the GPS leads Pelma Dilipy and Cherish Laiuetsou towards Binky


Joemar opted to hold the latitude line, which plunged the group directly into a thicket of Hibiscus tiliaceus. Pelma and Cherish sought a way around the thicket, to no avail. In the image on the left is a branch of Pterocarpus indicus and Macaranga carolinensis. On the right Carica papaya. 

Pelma Dilipy heads up a slope from a hidden valley.

Joemar would be first to Binky, which he gave to Pelma.


Rofino was neck-and-neck with Joemar, but at the edge of the paddle grass Rofino swung right looking for another way around the thicket. Joemar simply kept the latitude constant, no matter the terrain or obstacles..

Cherish, winded.

Pelma with Binky