The Weight Of My Balls

[RATTER15]

I have had an enquiry to make a concrete ball weighing 100kg. What diameter would this concrete ball need to be please. Its a side line of mine :-)

[Peter Pedant]

o god I cant believe someone convered a metric q
back into FPS - which we buried in 1972

[Hopkirk]

Do you need a mould?

[Khandro]

One litre of water weighs 1 kg. so the volume of the ball (if it was water) would be a 100 litres - after that tour de force I'm stuck.
I guess it would be about the size of a dustbin :0)

[Flonska]

Ratter

I think you will find that if you double the size, the weight will not itself simply double.

Assuming I am correct . . . using the previous example as a base, doubling the size of a concrete sphere to a diameter of 35.2" is likely to produce a mass which will weigh 1737 lb or 788kg

[RATTER15]

Yes Hopkirk, I will need a mould, I make the fibreglass moulds myself.

[malagabob]

And a gallon of water weighs 10 pounds.

[RATTER15]

Thanks everybody I have got back to guy and await his response. I have actually just made a 400mm mould for someone else, I may need to make another now.

[RATTER15]

Fitzer, Im sorry I have to take away your BA. I think.

I have a 340mm concrete ball made of standard concrete that weighs 40.1 kg (I have just weighed it)
Which unfortunately throws your calculation to the wind somewhat!

[jackthehat]

That's because none of us know what 'recipe' you are using for the mix, Ratter....

[IJKLM]

For Funks Sake, this is such an easy one.

Unreinforced concrete has a density of around 2400 kg/cubic metre

If you add steel reinforcement, then it depends on the amount of steel (which has a density of around 7800 kg/cu.m

Assuming unreinforced, 100 kg would reguire a volume of 1/24 of a cu.m or 1,000,000/24 cu. Cm = 41667 cm3

A sphere has a volume of 4/3 πr^3, so the sphere of 100 kg has a radius (not diameter) of cube root of 1,000,000/32π = 9947

So your answer is radius 21.5cm or diameter 43cm (16.9 inches)

If I work that backwards, it gives you 99.91 kg

Accurate enough for you?

[RATTER15]

JTH, I dont think the weight is going to vary a lot with standard concrete mix of 6 ballast to 1 cement, maybe a kg or two, I dont need anything that accurate. but of course I do need the dry weight not the weight of the wet concrete which of course would be much heavier due to the water content.

[IJKLM]

And if your 340mm ball weighs 40.1 kg, then you eed to divide 100 by 4.01 and take the cube root (tat's 1.356) then multiply that by the 340mm diameter, to give 462mm diameter for the 100kg ball to the same recipe.

[RATTER15]

IJKLM, that sounds more like it, many thanks!

[IJKLM]

sorry - typing too fast 461mm”

[anneasquith]

Jeez oh ratter, that's a huge ball.. !!!!!!