Looking for something besides water that is easy to handle, clean, and will fairly accurately represent the volume of objects when displaced. Small plastic BB’s is the first thing that comes to mind anything else that might be easy to acquire? I am concerned the BB’s might loose some accuracy by “packing” not sure how much round objects “pack”
You biggest problem with the bbs will be the pore space which is related to the packing. Most likely you’ll have36% of your space as air that you wont be able to measure after you push out the bbs. If you’re willing to have such a large margin or error im not sure why you wouldn’t just measure and call it good.
To decrease that you’ll need a liquid. Water is nice because its easy to clean and relatively unreactive. Since you don’t want water maybe a wax solution will work as long as what you’re measuring doesn’t mind a little of heat.
How about flour, or very fine sand? I will assume you don’t want to use anything liquid, but you can use solids of much smaller granularity that they approach the behavior of a liquid in terms of density.
I don’t think packing is necessarily a problem with the BBs. Assuming you calibrate yourself by, for example, putting all your BBs into a measuring beaker, with and without the object, that takes care of itself. Note that there are ways that liquid molecules pack, too, and for example adding alcohol and water produces a mixture with less volume than the ingredients. I think that only if there is a lot of pore space slightly smaller than the BBs will they be a problem. If you try to measure the volume of aluminum in a heat sink whose fin separations are a bit smaller than BBs, or for that matter a small integer multiple of BB size, will packing be a problem.
How much do you need the method, and what kind of expense do you accept? For example, would having a big pressure vessel and adding a known mass of air to it with the object inside, to measure the pressure increase, be acceptable?
HoneyBadgerDC - a little more information could help. Things like :
- Roughly, how big is the object you are trying to measure ? Is it roughly 1x1x1 inches or smaller or larger ?
- What’s your objection to water ? Is it because the object needs to stay dry ?
- How accurate should the measure be ?
Here are also some things to try :
- Free flowing particulates : Baby powder (talc ), Bentonite (gasoline absorbing clay)
- Liquids : Mercury (knowing it’s hazards), Galium, Silicone Oil, Lubricating Oil, Alcohol
- Finally - if the object is small enough. You may take some modeling clay or putty, do a rough mold around the object. Then you can fill up the mold with any liquid and measure the volume.
Wishing you lots of fun
The margin of error due to packing efficiency is not 36%. The margin of error is how much that number varies. If the packing efficiency is 36% +/- 2%, then the margin of error is 2%. This should be easy to experiment, just pour it into several different measuring cups, and multiple times, and see how consistent the number is.
Another source of error is that BBs will not conform around features that are smaller than the BB. So it will be very accurate for objects whose features (size of the smallest protrusions or dimples) are much larger than the BB. If you are measuring an object with small features, you want to use something smaller. I’m sure you can find bags of small plastic pellets that are smaller.
p.s. it would help if you told us what the object is, or at least what material it’s made of. “Easy to clean” depends on surface material. E.g. sand would work fine for non-porous surfaces, but not fabric.
For readily available products - I think ordinary table/cooking salt would be a good substitute - whatever you use would need a good shake and be absolutely dry.
I am measuring the volume of wood in the working parts of an all wood archery bow limb. Dyness is important. Salt might be the ticket here. I will check and see how much it packs. I would like better than 5% accuracy if possible, anything worse than that would make the experiments pretty useless. 2% accuracy would be great.
I would take a PVC pipe not much bigger diameter than the bow, maybe bend it a little so the bow can slide it (the bend in PVC can be achieved with a slight heating). The pvc pipe should be around 6 inches longer than the bow. Cap one end of the PVC and fill it up with motor oil. Insert your bow into the PVC pipe and measure the volume of oil that comes out
You can wipe the oil off the bow once you are done.
Both salt and oil could be absorbed by the wood and affecting it’s properties, although maybe not greatly enough to matter if done quickly, and the wood might even benefit in some way from either one. The plastic BBs may be able to stay within 2% accuracy according to scr4. Certainly there are other substances with smaller particle sizes that would not interact with the wood in any way.
Also, how consistent is the density of this particular wood? If consistent enough simply weighing the parts may provide your answer.
How about glass blasting beads?
Sand?
Ultimately, a 3D laser scanner might be a more accurate way to determine the volume. From poking around on Amazon, there are a few that sell for less than a thousand dollars. Or, there are service bureaus that will scan something for you (including a few in Los Angeles).
Another thought (if you or someone you know built the bow) -
If you have a sample of the material left over, weigh the sample, displace sample in water to determine volume, weigh the bow, do math.
Addressing everyone at once here. The density of the wood varies greatly from tree to tree and I also use multiple species which vary greatly. The bows are made in 1 piece and the handles styles and weight vary greatly as well. Typically a handle will weight a bit more than 1/3 the weight of the bow, the denser the wood the larger percentage of weight the handle area will be and conversely less dense woods would have lighter handles. In theory the working limb sections should all weigh about the same for bows of the same length and draw weight even though the thickness and width might be quite different. The elasticity of a particular specimen has a bigger impact on the mass weight than the density as different elasticity’s will require different dimensions.
Just for reference the typical displacement would roughly be somewhere between 12 and 16 cubic inches, so accuracy to less than 1/2 cubic inch would be nice.
How about an over-engineered solution??
Place the object into an airtight container.
Remove all the air with a vacuum pump.
Introduce a known volume of some gas, nitrogen for instance.
Measure the temperature and pressure of the gas in the container.
Calculate the volume of your object from the previous measurements and the known volume of the container.
Make silicone mold of bow.
Fill mold with water.
Measure water.
How about wrapping it tightly in clingfilm (saran wrap) and using water?
If you think it’ll make a noticeable difference, weigh it beforehand and you can adjust your answer accordingly. Or use a measured size and weigh a similar piece afterwards as the original bit may have water clinging to it and it’s dry weight be difficult to determine.
This thread reminds me of how they were attempting to measure the size of the cranial cavity in the 1800s: they came up with using pepper, IIRC.
A bigger brain cavity meant a bigger brain, therefore, a smarter kind of individual.
However, pepper…being a somewhat fluffy powder, was a bit compressible. The researchers were (not so) inadvertently packing the caucasian skulls tightly and the negro skulls loosely. :rolleyes:
Eventually, the pepper was replaced by using lead shot…a commonly available mass of pellets of reasonably uniform size and weight.