Making your own Mass Balance

Use a few coat hangers and BBs to weigh to 1/10 gram!

One coat hanger makes the stand, and another forms the balance. Parts of another coat hanger make the medicine cup holders (Dixie cups would also work).

Here's a detail of the base:


Make the balance part by straightening the hook and reshaping a hanger, use needle nose pliers, to look like:


Here's a detail showing the top part. Note the counter weight. When you get it all done the pointer will not point straight down, so put a small weight on the high side.


Below is a detail of the end of the balance arm showing the cup holder hanging on it.


The picture below shows a cup and its holder.


Below shows a fine wire basket used to hold a rock or mineral specimen. To determine the specific gravity of something, you have to weigh it in air, then in water, and then divide the weight in air by the difference.


Below is where you read the scale. The zero marks the point of perfect balance. The paper is on a book that holds the stand down and brings the paper up to just below the pointer. Note the two weights made from hanger wire. The small one is a 10.0 BB weight and the bigger one is a 20.0 BB weight. A 5, 50, and 100 BB counter weight would also come in handy when measuring heavier objects or fluids.


With the pointer at zero, add one BB to the cup the counter weights will go in. Mark where the pointer now points to. This interval is equal to one BB. Divide it into 10 parts. Now if you weigh something that is equal to the weight of 27 BBs plus a bit more (you had to use 28 BBs, but the 28th BB put the pointer past the zero mark), you can interpolate to the nearest tenth of a BB. Let's say you get 27.6 BBs. What's that in grams? Weigh something of known weight. Thirty milliliters of water weighs 30 grams, and let's say it took 88.0 BBs to balance it. So 30 grams/88 BBs=0.34 grams/BB. If one BB weighs 0.34 grams, then 27.6 BBs would weigh 9.4 grams (by multiplication) plus or minus 0.05 grams. Once you calibrate your scales to your BBs and calculate the conversion factor (0.34) you just weigh everything in BB units and if you want to know the weight in grams, just multiply the BB weight by 0.34 (or whatever).

Finally, here's another picture. Note the boxes under the cups that prevent them from going down too far when something is put in them.

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