How does a differential work?
 

http://www.youtube.com/watch?v=K4JhruinbWc

Before I watched this video, I knew what a differential did but didn't really understand how it did it. Now I know.

Nice, now I know.

that model/mockup of a cars rear end (tires, shafts, basic bearings and tinker-toy 'differential' is awesome.

Too bad that the simply mechanical elegance is being replaced by viscous couplings (that have many more failure points)

-John

That is the best visual explaination for how a differential works that I've ever seen. I like the trick riding in the begining, though I have no idea what that has to do with differentials.

That was brilliant. Thanks for posting it!

simple breakdown of how FWD works along with differentials http://www.youtube.com/watch?v=TlQ6KRqUepg

That is good. I first saw the principle of planetary gears in action with my old Saab 96. They had a weak clutch/tranny setup and I had the engine/transaxle out about 9 times over 6 years IIRC. A smarter man probably would have gotten rid of it.

I forget how exactly but when the tranny was opened up you could see the FWD differential. Cute as could be, all those well machined gears working so smoothly. A little bit of playing around with it and I could see how it worked and why vehicles w/o posi-traction or LSD can get stuck in the mud with the wheel with the least traction spinning.

I think with rear wheel drive cars, there's less opportunity to see the inner workings of the differential as it is rarely taken apart and repaired by the average guy.

When I played with Lego Technic models, that taught me how differentials worked (model 8880 was a Supercar that had 3 differentials, 4WD, 4-speed manual transmission and 4-wheel steering. That was a fun car to build.

Outstanding. The use of a rod to push both sides at the same time leads directly to the understanding of more spokes, and finally, gears doing the job.

Thanks for posting that!

Its no wonder kids were smarter/more science oriented back then, the emphasis on learning stuff like that was much higher.

Parents and educators thought less of the poor little dears' self image, and more one "hard" science, and truth. Truths like--the race goes to the swift. Not everyone wins; not everyone excels.

I think it has less to do with time and place and more to do with a sharp person who understood differntials and knew how to communicate that knowledge effectively in a very simple manner. I think that a pretty high percentage of people who knew exactly how and why differentials worked couldn't have come up with that simple model to explain it to the ignorant.
I've looked at a number of differentials in my day, saw what was happening but didn't understand it.

Now they just need to make one of those for an inline injection pump.

Differentials have been in use since the earliest days of the automobile, so I am guessing that the operation was pretty obvious to those pioneers.

The genius is the guy who first thought of the idea. I wonder what was the original problem that was the impetus for someone to create this solution. I bet it predates the need to have one wheel of a driven axle go faster than the other on a curve.

Another favorite canard of the right.

. . . thought less of the poor little dears' self image . . .

People can get damaged for life by overbearing, cruel people. Why are some people filled with self-confidence and courage while others are afraid to take risks? A bit of attention to this subject strikes me as a worthy task.

That was some pretty nifty model making in that piece. Someone put some time into that.

Last Friday night during the rain I did a 90* on the 110 freeway off/on ramp towards the 101 and landed face up on a mud hill facing the 101 above me.

What I think happened was that when coming out of the curve I gave to much gas and at the same time hitting a large pile of dirt/mud on the pavement making the drivers side rear wheel spin. The psg side rear wheel doing all the work now pushing me to the left of the the road doing a 90* upwards off the road.

Would a "Limited slip differential" have made a difference?

I would think probably but I'm not certain.

The Differential and YOU!

One of the things that annoys me from old news reels is the music. Old WW2 reels had the worst music underneath.

That however was one of the best videos I have ever seen.

A little attention, OK, but not at the cost of real achievement, or success. Not keeping score, giving everyone a participation award, giving inflated grades really doesn't fool anyone. The kids know who are the smart ones, and who aren't.

This business of giving out trophies for showing up was not run by me for approval in advance. It has gotten a bit overmuch. But this notion is raised all the times by critics of public education, none of whom are willing to put up with the grief of being a teacher for $50K or less per year.

Let Limbaugh try to teach in public schools for 5 years, I mean really try and I'll give the malarkey that he spouts and righties one and all parrot some credence.

My wife is a certified substitute teacher with a BS degree. I hear the horror stories every day she subs. One of my best friends is a career teacher, so I have a pretty good idea of what goes on in school.
I wouldn't last half a day before being up on assault charges.
The kids know that ALL the rules favor them, and that there are no consequences for any of their behavior. Even if the get suspended--its what they want-- no school. Their parents are illiterate, and do not encourage their children. One older sibling actually pays his kid brother for failing tests and getting into trouble. With family like that, how can anyone suceed?

I thought they were gonna use motorcycles to explain the whole damn thing, but anyway, the spokes explanation was pretty good.

Well, they did use the motorcycles to demonstrate how the outside wheel travels farther, and faster than the inside wheel. Other than that, I saw no purpose, other than entertainment value, to the stunt riders.

It goes along with what I've always said about the biggest problems in learning mathematics is that it's almost always taught by mathematicians.

might it have started with Roosevelt's "New Deal" and then progressed onward and downward with LBJ's "the Great Society"? the powers that be have determined that the children should be not held responsible for anything. as a matter of fact, the school system has done a 180 in that the system now REWARDS little Johnnie and Susie for acting out.

several years ago, I met a retired school teacher who had spent 30+ years teaching in the public school system. she said teaching jobs had been converted to baby sitting jobs. emphasis on the baby part.

when people offload their parental responsibilities to the "state", why are they surprised when it doesn't turn out well?

just curious on this one. does the W126 have a limited slip differential and might it make a difference in this type of situation?

I've sat on a number of math hiring committees and have been repeatedly impressed by the inability of highly educated mathematicians to teach their way out of a paper bag. I can remember one committee which tasked all candidates to teach a twenty minute lesson on a limit in calculus. The only one that made any sense began with "Imagine an apple pie in an oven. . ." He got the job.

I must have had one of the other candidates as my calculus instructor.

With the mindset of the system teaching to the high value test, the concept of how or why something works is given short shrift.

I had this one guy. Someone would ask him a question. He'd turn around and stare at the chalkboard for 2-3 minutes, sometimes even longer. Then he'd turn around and say something like "see, it's obvious" and stare at you.

This isn't a new problem.

I have a farm hand working for me. Clever guy...good with tools, takes care of the equipment, thinks about the next step (probably more than I do) and is motivated to keep on task and busy..

But, he's 45 and can barely read...he told me that basically he skipped class for 8 years and still somehow managed to graduate. Granted, he has a role in the problem but I do believe that the 'system' has a responsibility as well and in this case, Ruben was let down. IMHO, whomever let that happen needs a good, hard b*tchslap.

Apparently, you and I had the same algebra 'teacher'. Algebra might as well be Chinese to me and I LOVE numbers.

It's tough to teach math well. Unfortunately, most students don't think like mathematicians; and most mathematicians can't imagine how anyone could fail to understand the basics of math. I even have trouble helping my kids with high school algebra, it takes a lot of work to put yourself in the shoes of someone who just doesn't get it and doesn't even understand the language that you are using to explain it. Sometimes I think the best math teachers are people who only know a little more than the students.

Engineering math (as opposed to pure math) might even be worse, because they tend to teach what is required to solve certain types of problems without teaching the fundamentals of the underlying math. I was in grad school before I "really" understood some of the math that I had been using for years; I'm not sure I really understand some of it now, even though I know how to use it.

I have the same thing, I love playing with numbers and I can be pretty good at it times. Up to 2 months before my finals in High School I never had a teacher that inspired me. Fortunately I was blessed that prior to my finals we had a substitute that made all the "nonsense" I was starring at for the last couple of years clear to me. The algebra and engineering math finals were a breeze, surprised every body, including my self.

Math seems to be one of those subjects where students just "get it" all of a sudden and say, "why didn't you just say that before?" The problem is trying to find the key for each individual student to be able to "see through" all the noise and actually understand it. It's like one of those 3D pictures that are hard to see until you finally focus correctly; try to explain how to see that image to someone who just doesn't see it.

I think you're probably right there.

Funny that you say that. I had a Tae Kwon Do instructor in college who was also a professor of materials engineering. One day in class he mentioned how as an undergraduate he had nearly failed a class call emag (Electricity and Magnetism). He finally stopped trying to understand what was going on and just learned the formulas and how to apply them. I just happened to be taking that class at the time, and doing badly. I took his approach and suddenly started getting good grades in that class.

Math is an odd thing in the educational system. Everyone in Colorado colleges has to take a math course. Incoming college students without an ACT or SAT score which qualifies them for a college level course has to take a national placement test called Accuplacer. I decided to take it last week. I enjoyed Math in high school, hadn't take Algebra since 8th or 9th grade, took a wimpy Math for Liberal Arts in college and haven't done anything since so I thought I'd be good test case. I got a 77 on the test (not out of 100% and I don't know how the score is calculated). High enough to get me into College Algebra in some colleges or states, but not quite high enough in Colorado. It placed me in Intermediate Algebra.
However, here's the bizarre part. The test was only twelve questions and was multiple choice. (claims to be adaptive in giving harder or easier questions based on prior answers). Accuplacer will not tell you which ones you got right/wrong. The difference in one answer (good guess or bad guess) is enough to admit/deny a student into a college level math class. There is aboslutely no way for the test taker, who is the only one who knows shy a specific answer was chosen, to know if his or her reasoning process were correct or not.
There are probably hundreds of thousands of people having their college math possibilities controlled by this test every year. The owner of the test is making millions.

Another example of the difference between announced, and "real" goals. The fiels of professional education seems particularly to illustrate these.
The announced goal of the Accuplacer test is to correctly, ( and accurately) place a prospective student in the proper level of math. A good, and lauidable goal. However, the "real" goal of Accuplacer is simply to create wealth for its inventor.
Same story in many education endeavors. The announced goal is to fully educate our children, while the "real" goal is financial gain for the administrators.
Too bad.

and isn't it painfully obvious that with only twelve questions, the outcome may not be representative of the test taker's skills? and since they don't let you know which questions were answered correctly, this further handicaps the test takers. the test should be at least 100 questions and the test taker should be given the complete outcome including answers to missed questions. of course, they like to say, no, because then it opens the door to "cheaters". as long as they periodically change the questions on the exam, the cheater problem is eliminated. therefore there appears to be another agenda at play........

Preventing cheating would be the announced goal.
The "real" answer is that it empowers the testing administration, and similarly, dimishes the power of the test-taker.

yeah, I hated that test.. it screwed me over. I did great in highschool calc but that damn test put me in intermediate algebra. I stormed into the deans office or who ever it was at school and waved my high school transcript in his face. I ended up being stuck in college algebra.

as in all things, some will understand math better than others. I've been spending some time talking with some old timers and it appears that in some ways the educational system was better at teaching EVERYTHING in days past.......

it was just beginning to take a nose dive during my days in school (I'm in my mid-50s) and beginning with Generation-X has REALLY begun to to spiral downward.....

who knows what the future holds for education in this country....it doesn't appear to be positive, though.

My father had to quit school in the 8th grade to run his family's farm. He still seemed more aware of the world around him than most. The last word I word have ever used to describe his would have been," ignorant". ( if he had heard me utter such a thing, it might REALLY have bben the last word I ever said...:)) He had a grasp of trig that simply amazed me--it was like he understood all the relationships and used them as if they were life-long friends.

If you get asked an algebra question it's understood that you at least know some pre-algebra. If you get it wrong you get asked a similiar one, then they drop it to a pre-algebra question which assumes you know, uh, PEMDAS or something, and if you get it wrong...
.
.
etc.

good example of the public education system at it's finest, thank you for sharing it. the whomever you refer to are those who have designed, implemented and are operating the public school system. obviously on some level, it is failing us all. little Johnnie and little Susie are graduating with a diploma in hand and yet do not understand the basics.

prime example:

a few years back a television reporter was interviewing a brand new high school graduate. he asked the young woman the following question:

REPORTER: "Now that you are an educated high school graduate, may I ask a question concerning geography?"

YOUNG WOMAN: "Yes"

REPORTER: "Ok, then, what countries geographically border the United States?

YOUNG WOMAN: "What kind of a stupid question is that?"