Thursday, September 29, 2016

Thinking Of an Experiment

In my last three posts (which have conveniently been combined onto a single page in the tabs), I proposed three tests which anyone with modest resources could perform to show whether or not the Earth is flat. But lately I've been wondering if there is a similarly simple experiment that would show that the Earth is turning.

Not that a moving Earth and a sphere Earth are the same issue; educated people knew that the world was spherical long before they could tell if it moved or not. Some early thinkers, most notably Aristarchus, argued for a heliocentric model thousands of years ago, but it wasn't until the time of Copernicus and Galileo that we started having observation evidence to back it up.

Now, of course, we have lots of evidence; our entire space program depends heavily on the motion of our world and all of our solar neighbors. But flat-Earthers don't believe in any of that.

What I'm more concerned with is thinking of a way that, without the observational skills of an astronomer or sophisticated and expensive equipment, an average person could conduct a test to show that the Earth is turning.

I know of one that I find convincing, involving the Coriolis Effect. These synchronized videos show the experiment. I had another thought, but there is a problem that I'm not sure how to get around.

First, the idea. What if two people, one living very far north or south of the equator, and the other at the equator, were to weigh a standard reference weight at their respective latitudes using an accurate (but inexpensive) jeweler's scale? The precision of the scale is enough to show the difference due to gravity as long as the weight has enough mass.

Let's say that the reference weight is 100 grams. In theory, at either pole the reference weight would weigh 100 grams, and at the equator it would weight about 99.7 grams. That would show that some force is counteracting gravity at the equator. Maybe the flat-Earthers would make something up, but it seems obvious to me that the counteracting force is centrifugal (yes, I know, it's a pseudo-force, but it ACTS like a force, and shows that movement is taking place).

But there is one problem I do not have enough knowledge to overcome: calibration of the scales. When you buy a precision scale, the first thing you normally do is calibrate the scale to a reference weight just like the one I'm talking about. But, of course, when you calibrate the scale, you'd be calibrating it to local gravity, and the comparison would be invalid.

So my question to anyone who understands scales very well is this: why do you calibrate the scale? Is it because no two are exactly the same? Is it because something happens during shipping? Or is it, in fact, because of local gravity? Do you see a way around my little problem?

I'd love to hear from someone with the necessary expertise, because if this could be done with a pair of inexpensive jeweler's scales and reference weights, I think it would make a good addition to the everyman-approach to first-hand knowledge of the shape and motion of the world we live on.

Please leave comments below; I'm truly interested in hearing your thoughts on this.


  1. Thank you for this blog. I've found your arguments all well thought out and comprehensive. I only just recently learned how deep this flat earth rabbit hole really goes, although I suppose it's not that deep since otherwise it would come out the bottom. But I digress.

    I'm not a physicist, but I am an engineer and do have to contend with instrument calibrations. Any measuring device has an associated resolution and error. Typically the more expensive the instrument, the tighter the resolution. In the case of scales, cheap ones only give you resolution down to the pounds. Higher resolution will tend to set you back more. The most accurate scales, often used for chemistry or anything where you need to accuracy to a milligram or less, are so sensitive that air pressure can even affect your measurement. You should always ensure that such a scale is leveled and zeroed at the location that you will be using it. I never really thought about it, but leveling and zeroing your scale would take into account local gravity, among other things. Since these types of scales are usually measuring mass, not weight, you need to account for that difference.

    Calibration is essentially the same idea. You check your instrument against one that has been certified to ensure that it is reading what it is supposed to be reading. Without a calibrated instrument, you can't be sure of the measurement, and certainly can't do comparisons. To account for error, it's always preferred to use the same instrument for comparison measurements.

    I hope that helps.

    1. If I use the same instrument, though, would I be able to, say, ship it over a long distance and trust the results, at least within the required resolution, which is not actually that fine? I figure that the difference between my location, around 45 degrees north, and the equator, should amount to about 1-1/2 percent, so that a half-kilo reference mass would vary in weight by about 5-8 grams, not a tiny amount.

      I'd love to have your thoughts on this.

  2. That's an interesting thought. The main thing here is the difference between mass and weight. Weight is a force, the product of the mass and the acceleration due to gravity. Our 0.5 kg mass will be the same no matter where you measure it. But the weight of that 0.5 kg sample could vary. I think the type of scale that you are talking about is going to measure mass, and therefore would need to be adjusted to find a new zero point if the scale is moved. I'm thinking that you would actually be more interested in a force gauge of some sort. A force gauge does not adjust for gravity. A good example would be a fish scale. You hang a fish from the hook on the scale and let it hang freely. Gravity acts on the fish and compresses a spring. The deflection of the spring is proportional to the force by the spring constant (d=k×F), which is known and used to calibrate the scale.

    Perhaps instead you could use a known mass, like your half kilo, and measure the weight at two different locations. I would use the same scale and same mass. The difference in spring deflection would be proportional to the difference in acceleration due to gravity [(d2-d1)=k×m×(g2-g1)]. I've never personally tried this, but the idea makes sense at least. You don't care about the difference in mass since there should be no difference. You want the difference between the force at each location.

    1. My question then is if there is something like a fish scale with an accuracy of, say, half a gram. Or if a scale like a jeweler's scale (as opposed to a precision lab instrument), if zeroed in one location and shipped, would serve as a device for measuring force.

  3. That's a good point. A quick search on Amazon for force gauges says no, at least not without going into much more expensive units. A simple fish scale probably won't have that kind of resolution. The gauges I found have a readability of 50 kgf. You could use a larger mass though.

    A jeweler's scale could work. They say that they are measuring grams and ounces, but I don't know if that means they are really grams or if they are grams force. If you able to zero the scale and ship it without the zero getting moved, then it might work. I just don't know enough about how they work. I think they are actually balances, which remove gravity from the equation by shifting another mass.

    If the scale is sensitive enough, I would think that just going to a higher altitude would be enough to see a change. I would feel better about a larger mass since the percent decrease in weight would be larger. I'm sure a force gauge sensitive enough at that small of a resolution exists, but I'm sure it's not cheap. Since the whole point is to come up with an easy to do experiment, that might not work. I'd be surprised if there isn't a paper out there where someone has done this in a lab, but the people we are trying to convince aren't going to go read a science journal.

  4. "In theory, at either pole the reference weight would weigh 100 grams, and at the equator it would weight about 97 grams."

    Isn't it a 0.3% difference not a 3%?

    1. Yikes, you're right! I need to correct that. That's still a 300 milligram difference, which a jeweler's scale should have to problem with. That is, if shipping the scale wouldn't throw it out of calibration too much.

      Thanks for the heads up!


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