### RipStik linear motion and walking speed

On Monday I began the unit by asking the class to name words that they associated with the word "motion". This led to "walk, slow motion, time, distance, speed" in about that order. I added the word pace. I asked if there was a relationship between time and distance for a moving object. I did not provide definitions nor equations. I only asked. Then I suggested that we gather data to determine whether there was a relationship. I used a new fiberglass outdoor long tape on a hand cranked spool. This gave me 2500 centimeters to play with. I then, as usual, rode my RipStik timing distances every 300 cm except the final 2500 centimeter distance.

 time (s) distance (cm) speed acc 0 0 213.375 0 1.38 300 217 3 2.66 600 234 13 4.03 900 219 -11 5.28 1200 240 17 6.7 1500 211 -20 8.07 1800 219 6 9.59 2100 197 -14 11.94 2500 170 -11

My speed fell slightly along the route, especially in the final 400 cm, but overall my speed was about as steady as I tend to produce on the RipStik. Coasting is not an option over a twenty-five meter course, the board will slow due to friction, so pumping is necessary. The acceleration has a periodicity to it, that may be due to timing errors or may be a real effect related to swizzling the board.

On Wednesday I brought in the graph of the time versus distance data, showing that the data was linear, therefore a linear mathematical model was appropriate. I then built out the distance = velocity * time equation from the graph.

Walking out and back along the new tape

In an attempt to segue into a new homework and to make motion potentially more relevant, I used the Nike+ Running app to show that running apps report pace and not velocity. I then showed how pace was derived from the time in minutes divided by the distance in either kilometers or miles. I used the prior night's run as an example.

Distance 3.68  miles
Distance 592238.6 cm
Raw time 35 05 min sec
Time 35.0833 decimal minutes
Time 2105 s
Speed 281.35 cm/s
One km time 355.43 seconds
One km time 5 55 min sec
One mile is 160934 cm
One mile time 572.01 seconds
One time time 9 32 min sec

By the time I was done I realized that the presentation, and hence the upcoming homework, were probably too complex. I should not have added in the distance in miles nor the mile pace. My sense was that was a bridge too far, especially as the course avoids conversions.

Latched into the fire hydrant

That said, I am not keen on stripping out question seven of the homework. I think that still has relevance. The introducing of this topic, however, should parallel the upcoming participatory demonstration.

1. Did you walk or run on Wednesday?
2. How long was the duration of your walk or run in seconds?
3. How far did you walk or run in centimeters?
4. What is your walking or running speed in centimeters per second?
5. How does your speed compare to the 213 cm/s of the RipStik on Monday? Are you faster or slower?
6. One kilometer is 100,000 centimeters. The time in minutes and seconds to cover one kilometer is called your "kilometer pace." Calculate the duration of time in seconds for you to walk/run 100,000 centimeters. Convert to minutes and seconds. That is your kilometer pace.
7. One mile is 160,934 centimeters. The time in minutes and seconds to cover one mile is called your "mile pace." Calculate the duration of time in seconds for you to walk/run 160,934 centimeters. Convert to minutes and seconds. That is your mile pace.

I think the homework is not as confusing as my muddled presentation which started from my Nike+ Running app. That app is calibrated in miles. I should have used Adidas Train and Run which is calibrated in kilometers. That would have permitted a more straightforward pre-working of the homework from a speed in centimeters per second.

Inbound on a sunny hot day, no one opted to run

I stood at the fire hydrant and called off the seconds. This worked rather better than I expected.

3075 centimeters one way, 6150 cm round trip.

Times ranged from about 30 seconds to 63 seconds.