Rocking Chair Physics

[Touchwood]

Hi All,

Over the past couple of years a number of you have asked how I came up with the right curve for the rockers in my chairs..ie. a stable curve so when someone plops down in the rocker, it doesn't just roll and dump them out backwards.

After much research I've found the mathematical calculations needed to solve this , and have decided, after much consideration,to share them with you.

...and that's all there is to it. Just be careful of the "hopping hoop" solution.

:rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm::rotflm:

Don

 

[Trent Mason]

Ok. I don't think I want to ever try and build a rocking chair now. :no:

Although I wasn't able to follow you from the first sentence on, I appreciate you sharing this. If anything, I've gained the satisfaction of knowing that I know someone who understands all of that. :thumbs_up:thumbs_up :swoon:

 

[JackLeg]

I really appreciate the information,:icon_thum since, as you know, I make right many rockers. I've never had one dump anyone on their tookus:nah:, so I think I may have arrived at an alternate and possibly simpler solution.

It's called a 42" Radius!
:rotflm:

 

[Touchwood]

Hi Reggie,

This guy must be a real math-geek!!:gar-Bi

The half dozen rockers I've built used about the same radius as yours.

Strangely enough, if you look at his diagrams, having r about 1/2R looks about right. The problem is knowing where the "center of mass" is for the sitter, the R-r dimension. If we assume the tookus is about 16" off the floor, it would put the average center somewhere around 26". (now, be nice).

If you "do the math", R turns out to be 42":swoon:

I'm pretty sure this guy never built a rocker:nah::nah::nah::nah::nah::nah::nah:

Don

I really appreciate the information,:icon_thum since, as you know, I make right many rockers. I've never had one dump anyone on their tookus:nah:, so I think I may have arrived at an alternate and possibly simpler solution.
for the sitter
It's called a 42" Radius!
:rotflm:

 

[shopsmithtom]

Great work! I concur with your formula except that total energy is not a constant. Please re do this equation with that in mind & re post. I'm looking forward to the revision. -SST

 

[JackLeg]

[I'm glad there are folks who can "do that math" but I'll stick with good old T&E! :icon_scra You're correct that the average "tookus" height is 16" off the floor. AVERAGE, mind you! :confused_ Thaks for the affirmation. I was beginning to doubt my own methods!! :rotflm:][/B]

 

[jhreed]

Don, I have checked my wife's MASS and it is quite a lot over a "bit". so I guess I will just keep trying to make gliders. I have the plans for a double glider that should be just about right for her MASS.

James

 

[Bill Clemmons]

Don, when building a child's rocker (for a much smaller tookus), which part of the formula do you normally adjust before recalculating? Since I'm certain you have all this worked out in your brain, would you mind giving me the answer for a 3 year old? :gar-La;:gar-La;:gar-La; For a minute there I thought you were going to come up w/ E=MC2. :gar-Bi

Bill

 

[Touchwood]

Bill,

e=mcc only applies if your child can move at the speed of light (which, at times, they all seem to be able to do.... instantaneously)...in which case her mass and the rocker combined would expand to fill the universe. :nah:

This would not be good, so let's not try it:swoon:

If you just scale the rocker chair dimensions to suit the smaller body, the same 42"-44" radius is probably OK..you just shorten the length of the arc so the legs fit in a good place. You set the smaller chair on the standard size rockers and find the right "lean back" position, mark the leg locations and cut the rockers to suit...probably make them a bit longer in the back..kids really like to "rock".

On the other hand, I guess you could build the little chair and set it on the big rockers..and she would love you forever.

Daddy, watch this...Weeeeeee!!!!:rotflm:

:nah::nah::nah::nah::nah::nah:


Don

Don, when building a child's rocker (for a much smaller tookus), which part of the formula do you normally adjust before recalculating? Since I'm certain you have all this worked out in your brain, would you mind giving me the answer for a 3 year old? :gar-La;:gar-La;:gar-La; For a minute there I thought you were going to come up w/ E=MC2. :gar-Bi

Bill

 

[Touchwood]

Actually Tom,

...According to the Newtonian conservation of energy theory..it IS a constant...unless you want to get into that whole Einsteinian thing about energy and mass being the same if you move the mass fast enough ..but if you do that you get into really big bang stuff!!!!:nah:

Jeez...nuclear rockers!!!:rotflm::rotflm::rotflm::rotflm:

Tom,..I really don't have a clue about where this guy was heading with all the differential calculus

It's just amazes me that someone would take the time to do it. Like Jackleg said...42" works.

Don

Great work! I concur with your formula except that total energy is not a constant. Please re do this equation with that in mind & re post. I'm looking forward to the revision. -SST

 

[ehpoole]

You know, in college I left electrical engineering because I was sick and tired of Calculus (and had NO interest in differentials)... settled for computer science instead (where we had to master Turing machines and writing logic proofs -- go figure! Still better than differentials IMHO!).

Now, just when I was thinking that woodworking would be a safe hobby, someone like Touchwood has to come along and ruin it. :help:

Now I'm going to have to take up a simpler hobby; anyone else want to join me and pursue a hobby in quantum physics? How about string theory? :rotflm:

I'm afraid to ask what Touchwood could dig up on candle making?

 

[Joe Scharle]

Actually, had you read "The Hitcher's Guide to the Galaxy", you would know that the answer to life and all other questions is : 42 :gar-La;

 

[shopsmithtom]

All math aside, (mostly, at this point in my life, it just gives me a headache) I'm planning to try building a rocking chair soon & my plan was to set my (somewhat) old butt in a few chairs & find one that feels comfortable, and design around those dimensions...that way, no aching head or aching butt. -SST

 

[JackLeg]

All math aside, (mostly, at this point in my life, it just gives me a headache) I'm planning to try building a rocking chair soon & my plan was to set my (somewhat) old butt in a few chairs & find one that feels comfortable, and design around those dimensions...that way, no aching head or aching butt. -SST

SST, for comfort, I'll put my "redesign" up against most anything else. :icon_thum I've had people sit in them for 4+ hours and do just fine! If you were a little closer, you could come by and help me make some!! :wsmile:

Mine is roomy enough to accomodate a BUT big as a TUB! :rotflm:

 

[shopsmithtom]

JackLeg, If I were closer, I'd be happy to help. Someday, though, I'm hoping to be close enough to do that. -SST