What is the specific gravity of an ordinary potato?

Answer

Nice question, especially since you want to do it yourself at home!

You could easily determine that yourself at home: first you weigh the potato. Then you take a measuring glass and fill it with water. If you now put the potato in the measuring glass, the water will rise. This way you know the volume of the potato. Then just specific weight = mass / volume.

The digital scale is accurate to 1 gram. However, I think that the accuracy of a kitchen measuring glass will not be enough. Therefore a way without.

– Take a measuring glass, put it on the scale and then set the scale to zero.

– Fill with water to a clear mark as high as possible and write down the weight G1. That is now the weight of the water in the glass. The volume is V (but you don’t know that)

– Drain the water, add the potato, and top up with water to the same mark. Now you have a weight G2

Suppose the potato has a volume Va and a weight Ga. The specific gravity of water is, as you know, 1 gram/cm3.

In the first case you have:

G1 = V . 1 (because everything was water)

In the second case you have:

G2 = ( V – Va ) . 1 + Go

Insert the first equation into the second:

G2 = G1 – Va + Ga

the only unknown here is Va, the volume of the potato. So you can determine that. You already have the weight of the potato, so:

specific weight potato = Ga / Va

I tried it once and find 1.043 gr/cm3. The problem is that this kitchen method becomes less accurate as the specific weight to be measured is closer to 1, and that is the case here. I estimate that the final result has an uncertainty of 1 to 2 percent. But hey, the result is what it is. Sources on the internet give a slightly higher value, but it seems that the age of the potato also plays a role: the density decreases with age. Also be careful with values ​​of approximately 0.70 that you sometimes find. This is a guide value for the transport of potatoes in bulk, so with air in between.

Have fun with it!