Comments on: Developing The Question: Bike Dots

By: Marcia Weinhold

Marcia Weinhold — Wed, 27 Aug 2014 21:27:10 +0000

Is there any way to slow down the motion? I think the bike-less portion is too short for anyone to follow all four motions long enough to see any relationships.

By: James Key

James Key — Wed, 27 Aug 2014 16:11:05 +0000

Love the video and the whole series. Perhaps a small improvement (in the spirit of “developing the question”) would be to show the bike with no dots, and ask *the students* what we could pay attention to. Maybe you lead with, “We’re going to be learning about things that move. Some things move in a straight line, and other things move in a circular pattern. Other kinds of motion are possible, but these two in particular are especially easy for us to study. With that in mind, watch this short video clip, and be prepared to tell me — what things are moving in a circular pattern? Anything moving in a straight line?”

The intent here is for students to identify the dots *themselves,* and then you can be like, “Here are some dots that I thought would be neat to watch for our lesson today.”

Keep up all your trailblazing.

By: Nadine Herbst

Nadine Herbst — Wed, 27 Aug 2014 12:16:59 +0000

These are the folks in my department! I am teaching linear and angular velocity today and was going to show this video. I’ll give the kids the link to your questions and have you answer if you provide me with the student feedback.

I think I’ll also develop a google form of my own just like yours.

By: Dan Meyer

Dan Meyer — Wed, 27 Aug 2014 03:07:30 +0000

I think I get your intent here, Travis. Feel free to download the video here. http://www.101qs.com/3122-bike-dots The initial frame won't show the bike.

By: travis

travis — Wed, 27 Aug 2014 02:35:11 +0000

Is there a way to make the ‘splash shot’ [the first frame] be bike-less?

By: Howard Phillips

Howard Phillips — Tue, 26 Aug 2014 22:52:42 +0000

Oops! I meant “a gold mine”.

By: Howard Phillips

Howard Phillips — Tue, 26 Aug 2014 22:52:02 +0000

There is a serious confusion between “speed” and “velocity”. Speed is a scalar, a simple number, and velocity is a vector quantity, with magnitude and direction. The two textbook samples just ignore this. I wonder whether any poor student would get that the average velocity of my house calculated between 9am yesterday and 9am today is zero. (It hasn’t gone anywhere!!).
Angular velocity appears to be used in place of angular speed or speed of rotation. That is, of course, rotation about the axis of rotation.
I like your bike example, especially as point D has a speed (constant) and an angular speed (not constant). This should cause some big discussion.

There are other horrors in the book excerpts. Does anybody want to express the angular speed of the earth in rads/sec, I always thought it was 1, in sensible units.

As for examples, a pre quartz clock is a minefield. I think they still make them in China!

By: ash

ash — Tue, 26 Aug 2014 22:51:52 +0000

Great video.
To take a different aproach, what about the concept of understanting gear ratios?
Judging by the low cadence in the video, I’m guessing the rider is in 53 tooth chainring on the front and possibly an 18 tooth sprocket at the back. 53:18 or 2.94 – ie dot A (the wheel) rotates 2.94 times for every rotation of dots B or C (the crank).
Given the rear wheel is 700c, the diameter including a standard 23mm tire, ~ 27″. we can calculate distance the bike would travel for the ratio of 53:18.
Intriguing is a discussion about why we have gears and the effectiveness of using this gear at different speeds and on different inclines/descents.

By: Dan Meyer

Dan Meyer — Tue, 26 Aug 2014 21:48:34 +0000

@Bob, love that activity. If I didn't feature it for Great Classroom Action, that's a huge oversight. Pushed it to the top post.

By: Bob Lochel

Bob Lochel — Tue, 26 Aug 2014 18:43:01 +0000

Dan, one of my favorite activities from my trig days are “trig whips”, an activity my colleague now uses all the time with all levels. The lessons, resources, and some video are on my blog: http://mathcoachblog.com/2012/10/02/experiencing-linear-and-angular-velocity/

I keep telling myself that I would love to try this activity with 50 kids on the football field, or even have kids consider the speed needed to make it happen.

Without some physical activity, some sense of the motion and what it is that is actually changing, then the problems become nothing more than plug and chug experiences.