Uncertainties with marbles

In this experiment, I will be measuring the diameter of six medium sized marbles, with strings and micrometer to find out the differences in measurements I get with measuring with strings and micrometer. In addition, I will also be investigating if all medium sized of marbles have different measurements. I predict that, by using string and measuring the string by a ruler in centimeters, the measurement I make won’t be as accurate as by using a micrometer.

This is because when you use the string method, therefore it moves around or keeps slipping off the marbles. It would be really hard to get a perfect measurement, and this might have an effect when comparing the sizes of medium marbles. As well as that, measuring with a ruler the accuracy is only 0.1cm (10-2m) compare to measuring with a micrometer which it keeps the object in place, and its accuracy is 0.01mm (10-3m). In addition, I think six different marbles will have different diameters which mean they won’t all be the same due to the process of making the marbles.

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This is measured in cm by using string, since we can’t measure diameter with string, this is how we find out diameter. Diameter=Circumference/ The reason why we can’t use the string to measure the diameter of a marble is because don’t know where half of a marble is. To find the diameter we first measured the circumference by using strings and measured it in ruler and then divided it by to get the diameter. The reason why it is not divide by half is because to get a circumference from diameter we need to times it by.

From my investigation I found out, when I measured with strings and then measured with micrometer, there isn’t much difference, but there are some do have differences. From the graph on the diameter it shows that for marble 1 and marble 4 it has the same results in measuring with string and micrometer, and this is not what I expected, because in my prediction I thought every measurement for strings and micrometer would be different.

Furthermore, I’ve found out that machine made marbles are not an exact same size. And machine made marbles can vary as much as 1/16 inches diameter depending on the manufacture, since it is made in a mold, so none of them will be exactly the same. In addition, machine made marbles are made through many processes, such as for the glass marbles that we measured, they were made by one of the mechanical technique which is dropping globules of molten glass into a groove that is made by 2 interlocking parallel screws, and then as the screws rotates the marbles travel along them and gradually being shaped into a sphere as it cools.

I think that the process of the marble creations can cause the size of each marble to be different, because the dropping of globules might not be all the same amount, and the groove might be not all in the exact size, and since it is a cheap product, its manufacture does not need to be the same. Also, marbles are just using for playing or decorating, so it is not that significant to make them all the same.

I’ve also discovered that if I measured a marble in different direction in micrometer or strings it gives me different measurements. I think this might be due to the surface of the marble, from our eye sight it might looked like it is actually circular, but actually it might not be circular, because it is a circle, no matter which direction I used to measure, they will all be the same.
As you can see with the micrometer it only shows a little different, it I convert this into centimeter, everything will be 1.6…cm, compared to by using the string, it goes in a range or 1.4 to 2.04cm.

From this experiment, I’ve learned that it is more accurate to measure with micrometer than string, because marbles are small which their unit would be more accurate to measure in millimeter than in centimeter. And for micrometer, I think since we are comparing the diameter, using micrometer would be more appropriate, because by using micrometer we can measure the diameter straight ahead, and it stays still.


The weaknesses from the experiment would be due to the limited equipments that are available in the physics room. Such as that, using strings to measure marbles are not that appropriate, because it slipped a lot, as well as using the school ruler, because ruler that we were using shows 0.1cm between each scale, but it would have been better if there is a ruler that shows smaller number between it.

Also the marbles that we have used in the physics room are used for a long time, because many of them were chipped or has crack on them, which I think it might affect the measurement because the surface is damaged. This shows that, if I could redo my experiment, I would buy a new marble, so the surface of the marbles is all the same. In addition, rather than complaining about this, I think I could have used 3 different kinds of ruler to measure the strings, as well as I could have look at the brand new marbles to see how the new ones are different from the used ones.

For some of the improvements on my lab if I could do it again, will be that I would use more devices to measure the size of marbles if there are other available equipments. And for the further investigation, I would try measure handmade marbles (if I can find it), and compare it with the machine made marbles, to see whether handmade marbles are all in the same size of is it the same as machine marbles, that all the sizes are different. And the most important thing was that, I think if I could do it again, I would change the uncertainty for the micrometer, because if the uncertainty for ruler is �0.05 and it wouldn’t be the same for the micrometer, it should have been smaller than that, so I think I might have made a mistake in the lap, but at the end I still got the result that I was expected.

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