This sounds so gorgeous! Can we see a picture?
Laura

David, when you say "weighs a lot" what do you mean? I'm trying to picture a solid sphere that size..... 75 pounds? 250 ?? An estimate will do fine here; no need to hoist that thing again!
Thanks,
Laura

Concrete weighs about 4000 pounds a cubic yard so get out your pencil.
Here is the formula.
volume=4/3¶r3

I expect this homework done by tomorrow.;-)

Remember.... I taught 5th grade. We were at the stage where we took foam and "built" a cubic foot model out of 12 one inch thick 12 by 12 squares. We did the same thing with a cubic yard. Most 10 year olds really don't understand this concept at a level where they can build on it but those who "got it" when working with the models thought it was really neat. I'm sure the others understood the concept in later grades as they were exposed to it again. While I pretty much understand the cubic concept, I don't recognize the symbol in your formula after the first 3. (could that mean pi??)

Also remember I am the one who found the formula for figuring the surface of a sphere and then used it to incorrectly determine a 52 inch ball would take 29 sq yards of mesh! (just one little mistake makes such a difference in math!)

I will work on the formula but I still think the person who built it will get closer guessing...

Laura

The formula : diameter cubed X 0,5236 . Just guessing, he used 11 gallons of heavy stuff, the perlite is light weight, how big is the bag of grout? Plus the water, it is approximately 50 liters or less. Sorry, Canada is metric! Using the formula and pencil, I got approx. 1,5 cubic ft for the volume . Maybe 150-200 lb?
Let us know!

Andrea

My son suggested that we get DW's bathroom scales and weigh the thing. I can just see me explaining why she won't be able to check her diet progress this week! The ball is heavy enough that I don't really want to pick it up again and it was much easier to let it fall to the grass from my shoulder than to set it down. I turned the cattle trough over while it was empty and rolled the sphere into it then set it upright and filled with water. (I'm not sure that a solid sphere needs this special curing. It is a perfect shape for avoiding stress points.) I think I'll rig up the boom pole on the tractor and pick it up with slings the next time.

I assumed that the WalMart ball was 16" so I calculated the volume to be around 9.5 gallons. As soon as I got this mixed (10 gal.) could see that it would not be enough so I quickly added 1 cement/1 perlite/2 sand. I had about 3/4 gallon left over. I will measure the sphere and let you know its actual size.

So, back to the fun stuff... MATH! Assuming an 18" sphere gives us (4 * 3.1415 * 729)/3 = 3053.538 cubic inches.
There are 46656 cu. in. in a cu. yd. which weighs, per tufaenough, 4000 lbs. So we have (4000 lbs. / 46656 cu. in.) = 0.0857 lbs./cu. in. Therefore, the sphere theoretically weighs (3053.538 * 0.0857) = 261.8 lbs. I don't think it weighs that much because I am certainly no he-man. The perlite takes away some and it probably is not a full 18" dia.

BTW, there is 231 cu. in. in a gallon so the 18" sphere should hold (3053.538/231) = 13.23 gallons; that's pretty close to what I have. Maybe I am a he-man....NAH!!!

David

David, you are a he-man any way you look at it. If the thing weighed even half what the math says you hefted 130 pounds up onto your poor shoulder! I am betting it was closer to 175 pounds since you are thinking of rigging up the tractor next time you move it.
Are you sure you wouldn't like to make a sphere out of the mesh/quickwall?? You could leave a little cork sized hole in the top. It is waterproof so you could pick the finished sphere up with one finger and carry it anywhere you wanted and then fill it with 9 gallons of water which would hold it down 60 -ish pounds worth. just an idea.....
Laura

OK,enough!
You would think that you guys didn't get enough in school!How does this do for a weight determination:
Heavy-can lift it with mild difficulty.Girls nearby aren't really impressed because they can lift it,too.
Real heavy-Mighty struggle to lift it.Girls suitably impressed.
Way too heavy-get it half way,then yield to the pain of a hernia.Girls lose interest and wander away.You,on the other hand,are trying to get your cellphone out to call 911.
There.THAT is the way to measure weight!
Cheers from here(snicker!)

I like it, Rickharmer. Probably most nations could adopt this as their standard unit of measure for weight. It has universal appeal since it leaves out mathmetical formulas and gets around all that metric/non metric problem. It would suit women because men get to do all the heavy lifting!
Laura

Okay. Today I measured the ball. The actual truth is 16" dia. @ 135 lbs. (wet). Now I've got to measure my measuring bucket; was I really putting in gallons of material? It sounds like I was a little short.

I don't know about impressing girls. I just know that none of them are asking me to wear fig leaves and laurels while pushing their spheres around in fields.

David,

I am also working with a POP mold on the huge walmart balls. I would like to figure out how to make a POP mold so I can cast balls that are smooth on the outside and hollow on the inside. Can we see a picture of your work? I am dying to get a visual.

Mary