Comments on: How A Differential Gear Works

By: Dale

Dale — Wed, 06 Apr 2011 05:37:48 +0000

I found it very effective. Clear, concise, stuck to one point and drove it home. I can see how someone with absolutely NO mechanical exposure at all might not “get” the transition to beveled gears at the end, but I think they’d *believe* that it works. IMO not everyone needs a rigorous undertanding of every nook and cranny of every device. “there’s some paired gears and they pivot without slipping and so the car can go forward AND turn without skidding” is more than enough for most people, most of the time.

Certainly gets me through most mechanisms I run into in everyday life. And I’m all edumacated & stuff.

By: Isegoria

Isegoria — Mon, 04 Apr 2011 16:42:31 +0000

I agree; videos and animations definitely have a role in explaining just about anything — and they work better when they think out loud. The illusion of understanding — or Discovery Channel Effect, as Aretae calls it — is fascinating though.

I could have sworn I’d posted something substantial on analog computers for fire-control systems before, but I can’t seem to find anything. Hmm…

By: Isegoria

Isegoria — Mon, 04 Apr 2011 16:39:04 +0000

I remember reading that when you posted it. I've also mentioned the south-pointing chariot before — a fascinating piece of technology that came arguably before its time.

By: Isegoria

Isegoria — Mon, 04 Apr 2011 16:15:35 +0000

I think you're correct that few people have preconceptions about differentials, so, by the framework, they should be open to learning. On the other hand, I definitely felt the Discovery Channel Effect wash over me as I watched the video. It all made perfect sense at the time, but I could only recount a tiny fraction of what I supposedly learned: the inner and outer wheels travel at different speeds during a turn; we can allow that while transferring power by cutting the axle, attaching spokes to each end, and placing a spoked wheel orthogonally between them; more spokes means more even power transfer, until they look like gears; etc. Also, yes, organizational learning is more about changing habits than instilling knowledge. We do what our habits dictate, even when we know better.

By: David Foster

David Foster — Sun, 03 Apr 2011 23:02:56 +0000

Also — the south-pointing chariot, invented in China circa 1000 BC, used a differential to keep track of absolute direction, regardless of the twists and turns the chariot followed.

By: David Foster

David Foster — Sun, 03 Apr 2011 22:58:24 +0000

Very nicely done — the video “thinks out loud” about the problem and the kind of issues one would face in trying to solve it. In general, videos and animations do have a legitimate role in explaining mechanisms and physical principles.

By the way, differentials can also add and subtract and were used for that purpose in mechanical analog computers, including fire-control systems, some of which were quite sophisticated.

By: Jose C Silva

Jose C Silva — Sun, 03 Apr 2011 15:45:07 +0000

No, I think this one is effective, because it addresses something that most people don’t have preconceptions about. Most people don’t notice the problem of different speeds necessary for a turn, which means they haven’t made a “intuitive” theory for it, and therefore will be open to learning.

Some “organizational learning” expert has a book that makes the case that the problem with [organization] learning is not getting new ideas in, it’s getting old ideas out. Alas, I don’t remember which expert or book.