Fun experiments to disprove Flat Earth

[accelerandom]

Hi everyone, I work at a small high school that does one-on-one teaching with students who often have some kind of attention related learning difficulty or have trouble in a large classroom. The physics and chemistry courses I have been teaching have very inadequate lab sections and we have very few lab materials, resources or suitable rooms. I've successfully hugely upgraded the chemistry labs by adapting experiments for a chemistry set. I need to do something similar for the physics labs...

One of my current students is doing physical science (and is not very interested or engaged). He noticed a poster of the Earth's core and made an odd comment - he had heard that maybe the Earth isn't really round (!). I suggested that we could incorporate this into the course.

I would like to do some fun experiments that can disprove or at least demonstrate evidence against "flat Earth theory" - whatever bizarre internet version is currently popular. I'm convinced most people who claim to believe it are joking, but I decided to take my student's value at face value because it might be fun to examine the claims and actually his interest.

Any suggestions? Even stuff that is only tangentially related to the consequences of the Earth's shape could be good, if I can tie it to the course goals. We can go outside but are very limited in equipment, though I can probably get permission to purchase anything not too specialized or too expensive. The course is a basic physical science one (introductory physics and chemistry) using Holt's Physical Science textbook.

 

[Vanadium 50]

How about the Earth's shadow at a lunar eclipse?

 

[OmCheeto]

I can't think of a classroom scale experiment that would prove the world is round.
The world is effectively flat at the classroom scale.

There are of course lots of "logical" explanations, based on things observed outside the classroom that tell us the world is round.

I would choose a mathematical approach to the absurdity of a flat earth.
For instance, they claim gravity is caused by the Earth accelerating. (Cavendish was obviously an early "round earth" conspirator)

Here's a rather naive, back of the hand calculation, that shows that the energy to accelerate an average high school student from birth to the speed they're at now exceeds the total world energy consumption for a year. I say naive, as, if you look closely at lines 7, 13, and 15, they are exceeding the speed of light. Perhaps you can have your student correct my maths.

 

[rootone]

Not an experiment as such, but you could refer to the ISS and many other satellites which have produced copious amounts of photographs of Earth,
also pointing out that those are ORBITING the Earth in order stay aloft, in a flat Earth scenario they would simply fall back to Earth immediately after launching.
It is possible (though probably not likely) that what the student meant is he heard that Earth is not an exact sphere, (it's a spheroid but is not wildly adrift from being a perfect sphere).

 

[CWatters]

Unfortunately flat earthers believe all such photos are fake and the ISS is in a hanger somewhere near area 51.

 

[Vanadium 50]

Two more ideas:

Focault pendulum - shows it's the Earth that rotates and not the stars

Direct measurement via surveying. This looks tricky - the Earth curves at about 8 inches per mile. If you had two towers 20 miles apart you could show that each one is 15 feet lower than the other.

 

[ZapperZ]

Hi everyone, I work at a small high school that does one-on-one teaching with students who often have some kind of attention related learning difficulty or have trouble in a large classroom. The physics and chemistry courses I have been teaching have very inadequate lab sections and we have very few lab materials, resources or suitable rooms. I've successfully hugely upgraded the chemistry labs by adapting experiments for a chemistry set. I need to do something similar for the physics labs...

One of my current students is doing physical science (and is not very interested or engaged). He noticed a poster of the Earth's core and made an odd comment - he had heard that maybe the Earth isn't really round (!). I suggested that we could incorporate this into the course.

I would like to do some fun experiments that can disprove or at least demonstrate evidence against "flat Earth theory" - whatever bizarre internet version is currently popular. I'm convinced most people who claim to believe it are joking, but I decided to take my student's value at face value because it might be fun to examine the claims and actually his interest.

Any suggestions? Even stuff that is only tangentially related to the consequences of the Earth's shape could be good, if I can tie it to the course goals. We can go outside but are very limited in equipment, though I can probably get permission to purchase anything not too specialized or too expensive. The course is a basic physical science one (introductory physics and chemistry) using Holt's Physical Science textbook.

What you can do is not an "experiment", but rather apply the "If this is true, then..." concept, and then compare it to what the students already know.

First of all, you need to establish a model for a "flat earth". This isn't as easy as it sounds because, just like creationism/intelligent design, it is difficult to nail down a consensus or unambiguous model. So you need to use the simplest model that you can find. We can easily start with the Earth being a flat disk, just like this picture below:

I am showing the sun out of scale. It should be very far away so that the light "rays" (yellow arrows) reaching the Earth is practically parallel.

Now, we also must establish that the Earth is spinning along some axis (a Foucault pendulum can clearly establish this unless one is at or close to the equator). To start, let's assume that it is spinning along the z-axis as shown.

The sun, based on our observation, not only goes across the sky, due to the spinning earth, but also has a different maximum inclination at different times of the year, due to the tilt of the axis of rotation. In this case, I'm showing it at some tilt in the sky in the drawing.

Once you have establish this, then we can play the game "If this is true, then...".

Ask your student that if this model is true, how does this compare to what we already know.

For example, the Earth having such a shape will have the same amount of sunlight throughout the ENTIRE surface at any given time. This means that everyone will either be having winter at the same time, or summer at the same time. This is because the amount of light reaching the surface per unit area will be the same everywhere (remember, the sun is very far away). So the heating of the surface of the Earth will be the same everywhere on the surface of a disk.

YET, we know that this is not true, that while some parts of the Earth are in the depth of winter, other parts of the Earth are in the peak of summer, while other regions of the Earth barely experience any seasonal change in temperature at all throughout the year. So already there is a problem with this flat Earth model.

Next, if this flat Earth model is true, then everyone will be seeing the sun at the same inclination above the horizon at the same time. After all, the light rays are impinging on the surface at the same angle everywhere.

Yet, we know that this is not true because we have time zones, and various parts of the world are at night while we are in daylight.

Etc...

Now, one may also change the axis of rotation to be along "r" instead. If one does this, then maybe a flat-earther will argue that people on the "underside" of the disk will have opposite time period, i.e. the side facing the sun is having daylight, the other side will be having night. But is this valid?

It isn't, because again, one side of the disk will ALL see sunrise, 12:00 noon, or sunset at the same instant. Yet, I know for a fact that the sun sets at different times in Chicago than in Fargo, ND.

And so on...

In other words, get your student to imagine the situation that the Earth is flat, and then figure out the consequences. The compare those consequences to what they already know and take for granted. You'll see that they do not match.

The most direct way to determine that the Earth is a sphere is to actually look at the precession of the Foucault pendulum at different latitudes over a period of 24 hrs. The precession angle goes from 360 degrees at the North Pole, to zero at the equator, to NEGATIVE 360 degrees at the South Pole, i.e. it precesses in the opposite direction as the North Pole. So if you or your students can find friends at various latitudes all over the earth, they can collect the data for you and you can compile this.

An indirect way to infer that the Earth is not flat like a pancake is to simply look at the heavens above. Grab a very good telescope, and one can look at the planets all around us. They all look spherical, even though we are very far (i.e. I'm acknowledging the "spherical cow"). Very good telescope will show you Saturn, Jupiter, Mars, etc. looking very "sphericallish". It would be extremely ODD that the Earth is FLAT when every celestial body we see around us are not.

So without actually doing an experiment, you can already get your students to think and apply what they already know to come up with a rational argument on why the Earth isn't flat.

Zz.

 

[TeethWhitener]

Field trip! This only works if you're near an ocean. Fill a balloon with helium and let it go. Let the students take note of how the balloon gets smaller and smaller until it's finally too small to discern. This is what happens to objects when they move in a straight line of sight away from you. Now get on a boat and start sailing out to sea (or alternately watch a boat as it goes out to sea). Pick a large landmark like a mountain or a tall building (or a "boatmark" like the hull of the boat) and watch what happens as it recedes. The base of the mountain/building/hull of the boat will disappear before the top of the structure. This indicates that the water between you and the structure is getting in the way of the line of sight. This can only happen if the surface of the water curves upward between you and your landmark.

Note that you've already done the control with the helium balloon: the students can't say that the disappearance of the base of the structure is simply how things look when they get further away. There has to be an extra factor that causes the water to block part of the structure but not all of it. This factor is the curvature of the earth. In fact, what I've described is one of the simplest (and oldest) arguments demonstrating the curvature of the earth--it was known to the ancient Phoenician and Greek mariners (and probably many other seafaring cultures as well).

Edit: the same principle applies when you drive westward toward the Rocky Mountains across the US Great Plains. You see the tops of the mountains long before you see their bases. But there someone might object that you're coming over a hill or some such nonsense. The advantage of doing this on the ocean is that most people will intuit that the ocean is as flat as something on Earth can possibly be--no hills can get in the way of you and your landmark.

Second edit: ooh, if you are in the middle of the country, you can combine the Rockies idea with @Vanadium 50 's surveying idea, so that if the students claim that they're simply coming over a hill, you can measure the "height" of the hill. Spoiler: it'll be related to the radius of the earth! The math might end up being a little advanced for high schoolers, but maybe not. You could walk them through it nonetheless.

 

[OmCheeto]

Field trip! ...

"No field trips allowed" is what I interpreted from:

too expensive

...
Edit: the same principle applies when you drive westward toward the Rocky Mountains across the US Great Plains. You see the tops of the mountains long before you see their bases. But there someone might object that you're coming over a hill or some such nonsense. The advantage of doing this on the ocean is that most people will intuit that the ocean is as flat as something on Earth can possibly be--no hills can get in the way of you and your landmark.

Second edit: ooh, if you are in the middle of the country, you can combine the Rockies idea with @Vanadium 50 's surveying idea, so that if the students claim that they're simply coming over a hill, you can measure the "height" of the hill. Spoiler: it'll be related to the radius of the earth! The math might end up being a little advanced for high schoolers, but maybe not. You could walk them through it nonetheless.

I was actually working on this idea last night.

A photograph (ref: wiki) from a local landmark included two mountains, with known distances and heights.

I was unfortunately not able to determine the horizontal elevation angles from the image. (I'm blaming it on "I should go to bed now")
Though, I was able to determine, with high school level maths, that Mt. Rainier should appear shorter in the image. (for a flat earth)

°
above
horizon   object
1.49      Mt. St. Helens
1.42      Mt. Rainier

I would figure out what the image would look like for a flat earth, but that would interrupt my nap.

 

[vela]

You could have the students time when the Sun disappears below the horizon. Students observing from the ground will see the Sun set before students who are on top of a building, for instance.

 

[tnich]

Next, if this flat Earth model is true, then everyone will be seeing the sun at the same inclination above the horizon at the same time. After all, the light rays are impinging on the surface at the same angle everywhere.

Yet, we know that this is not true because we have time zones, and various parts of the world are at night while we are in daylight.

If you teamed up with another physics class somewhere to the north or south of you, you could each measure the sun's inclination at the same time and repeat Eratosthenes procedure to calculate the circumference (or radius) of the earth.

 

[kent davidge]

As @tnich mentioned, one can repeat what Eratosthenes did some 2,500 years ago. (Though not in the original scale because I doubt one is easily going to travel 800 km.)

 

[rootone]

You don't need to travel though.
You could just phone an airport and ask what time it is according to them.
Then other airports.

 

[Vanadium 50]

ou could just phone an airport and ask what time it is according to them.

Time Zones?

 

[Greg Bernhardt]

Here are 7. Some already mentioned here.
https://www.pbs.org/newshour/science/7-diy-experiments-b-o-b-the-earth-is-round

 

[Janus]

Download and print a map of a "flat Earth" like this one
https://flatearthdisclosure.files.w...024px-azimuthal_equidistant_projection_sw.jpg

Pick two distant points on it and use a straight ruler mark a straight line between them. Note the path is takes over the surface of the map.

Take a globe and a piece of string and stretch the string along its surface and note its path.
Compare the results to a map of flight paths for the world like this
http://besttabletfor.me/wp-content/...ry-cool-map-of-world-composed-with-flight.jpg
Do this for several different paths.

Jets will fly the most direct and shortest path between two points. So which of methods above, Straight line on flat Earth, or string over surface of globe, matches the flight paths shown in the last image?

 

[itfitmewelltoo]

The original proof goes back to some hundred years BC. It involved shadows at noon in two locations. The result was marvelously accurate. Can it be scaled?

 

[OmCheeto]

Here are 7. Some already mentioned here.
https://www.pbs.org/newshour/science/7-diy-experiments-b-o-b-the-earth-is-round

#6

Experiment 6: Travel to space!
Things you’ll need: buckets of money
Space tourism is another option for those interested in seeing the Earth’s curves. The trip will cost upwards of $40 million...​

reminds me a bit of some googling I did yesterday.

Om's experiment 8: Travel to the south pole!
Cost: $53,400
[ref]​

Flat earthers claim the north pole is at the center of the world, the south pole is actually a perimeter wall, and that NASA was created to keep people away from "the wall".

Other fun things I learned while googling about the south pole:

"Google Earth" displays everything at the south pole as being at latitude 85°. (?)

Googling a reason for this, I interpolated what I was reading as: Mercator maps are hard to render on a sphere, so they just limit the latitude to 85°.
​

There are no airline flights over Antarctica.

Reason: Something called ETOPS. A rule that says airlines need to not stray too far from an airport along their path.​

Lots of other fun stuff!

As far as I can tell, nobody who has studied this for more than 10 minutes thinks the world is flat.
So I think "flat earthers" are just a bunch of people having fun with "recreational mathematics".

Two of the worst proponents, from my research, of the assertion "there are people who believe the world is flat!" were: Washington Irving, and Jean Antoine Letronne.

Irving, an American, claimed that Europeans were stupid, because they believed the world was flat. (Not true)
Letronne, an atheist, claimed theists were stupid, for the same reason. (Also, not true)​

 

[OmCheeto]

...stupid...

Reminds me of a conversation from a few years ago regarding the history of geocentric vs heliocentric views.

Om: I wonder why it took so long for the ancients to figure that out.
Bob: They were stupid.
Om: But what if the moon hadn't been tidally locked? I think that had a big influence.
Bob: Your stupid.
Om: You're.​

 

[accelerandom]

Thanks, everyone, for the responses. It seems like actual experiments may be mostly impractical. We are in the Seattle area but the sea isn't visible from the school, and the weather may make it too difficult to observe approaching ships, and I'm not sure there are enough miles of open sea for the effect to be noticeable. Also, I think the timing difference for the sun setting between the ground and a tall building may be too small to measure effectively.

However, something to do with time zones and comparing the positions of the sun using a distant friend and Skype may be feasible...

Also, the various thought experiments/logical arguments may be useful. Perhaps some can be illustrated/demonstrated with a light source and a model flat Earth and globe? In any case I think some combination of thought experiments with a long distance Skype observation might work...

 

[rootone]

Time Zones?

Well yes, but these are conventions which are useful for commerce and so on.
The time zone where I live now is in the same as the zone I was born in, but in fact there is about 45m difference in sunrise/set time.
It's something I actually checked out during a phone call one evening.

 

[Hamid438]

I guess for a flat Earth when it is night, it means every where on Earth is at night. We can proof the Earth is round by calling somebody that their time is opposite time to caller. Modern day verification.

 

[pinball1970]

I guess for a flat Earth when it is night, it means every where on Earth is at night. We can proof the Earth is round by calling somebody that their time is opposite time to caller. Modern day verification.

This is a very good modern day application

I think the fact the horizon looks the same distance now matter where you are on the planet is a good one, you only get that on sphere- accounting for such annoying features such as mountains, large buildings.

The boat coming over the horizon sail first is also good practical example along the same lines.

 

[Vanadium 50]

You could just phone an airport and ask what time it is according to them.

Time Zones?

What I expected you to say was "Whoops! Forgot about that!"

What instead you said was:

Well yes, but these are conventions which are useful for commerce and so on.

So let me make this clear. Your idea will not work. It's poorly considered, completely unhelpful, and the fact that your reaction is to defend it in light of this gobsmacking. Calling an airport in 2018 is not the same as calling - er...telegraphing - a railway station in the 19th century. (Aside: it was the telegraph that provoked the development of time zones)

 

[pinball1970]

We can go outside but are very limited in equipment

Does the student accept the Earth is rotating? That the moon is in orbit around the earth? Earth rotates around the sun?
A rotating globe and a torch can illustrate how night day comes about (close the curtains)
Images from Hubble voyager Cassini show that all the moons and planets are spherical as are images of the earth.

 

[pinball1970]

whatever bizarre internet version is currently popular. I'm convinced most people who claim to believe it are joking

They are not joking, they are as serious as the anti vaxers / evolution deniers, the have conferences...

Will you be updating the site with your results? His arguments?

 

[OmCheeto]

Thanks, everyone, for the responses. It seems like actual experiments may be mostly impractical. We are in the Seattle area but the sea isn't visible from the school, and the weather may make it too difficult to observe approaching ships, and I'm not sure there are enough miles of open sea for the effect to be noticeable.
...

My calculations tell me that the Seattle to Bremerton ferry will sink about 40 feet by the time it makes it's right turn. Of course, you would have to be watching from water level. Seems like that should be visible with binoculars, or better yet, a camera with a healthy zoom.

Someone at stackexchange described the experiment. It's the first response to someone's question; "How high up do you have to go before you can sense the curve of the earth?"

I'll have to remember to try and recreate the experiment this summer.

 

[Greg Bernhardt]

Neil deGrasse Tyson Disproves The Flat Earth Theory
http://www.techtimes.com/articles/2...sse-tyson-disproves-the-flat-earth-theory.htm

 

[OmCheeto]

Neil deGrasse Tyson Disproves The Flat Earth Theory
http://www.techtimes.com/articles/2...sse-tyson-disproves-the-flat-earth-theory.htm

WARNING!
DO NOT WATCH THE INCLUDED VIDEO TITLED:
Flat Earth - Bedford Level Experiment 2016
IT IS HOGWASH, FROM START TO FINISH.​

At least the title was a good reference to lead me to some things I hadn't considered, which might render my "Just look across the Puget Sound" experiment invalid.

From the wiki entry on the Bedford Level Experiment:

"If the measurement is close enough to the surface, light rays can curve downward at a rate equal to the mean curvature of the Earth's surface. In this case, the two effects of assumed curvature and refraction could cancel each other out and the Earth will appear flat in optical experiments."​

I found the following quite hilarious:

"On 25 July 1896, Ulysses Grant Morrow, ... conducted a similar experiment... he concluded that the Earth's surface was concavely curved... The findings were dismissed by critics as the result of atmospheric refraction."​

Not just flat, but bowl shaped!

I will have to think about this some more. The logistics of setting out 10 miles worth of buoys sounds like a nightmare.

 

[zuz]

Do like the ancients did. If you live near a large body of water, observe ships coming in or out over the horizon. You will first see the top of the ship and gradually the entire vessel will come into view, proving without a doubt the curvature of the Earth.

 

[JohnNemo]

I would like to do some fun experiments that can disprove or at least demonstrate evidence against "flat Earth theory" - whatever bizarre internet version is currently popular. I'm convinced most people who claim to believe it are joking, but I decided to take my student's value at face value because it might be fun to examine the claims and actually his interest.

You could link up with a few other schools at varying distances to the south of you. They don't have to be due south - south west or south east, or a combination, is absolutely fine, so you could choose Florida, then southern Mexico (or Barbados if you want an Anglophone country) etc.

Get students at each school to measure the angle of the North Star. You don't need exact measurements. You could, for example, have one student raise their arm pointing to the North Star and have another student photograph the first student's raised arm so you can see the approximate angle.

The further south you are, the lower in the sky the North Star will be, then when you are south of the equator the North Star will not be visible but the Southern Cross will be, getting higher in the sky the further south you go.

 

[accelerandom]

Ah, now I remember reading about the Bedford experiment and atmospheric refraction a few years ago... annoying that that probably makes the Bremerton ferry watching unfeasible. I will work with my student to plan some kind of project that will probably involve Skyping or otherwise communicating people in different latitudes and longitudes and noting the stellar and solar differences between here and there. Thanks again everyone for the suggestions and links.

They are not joking, they are as serious as the anti vaxers / evolution deniers, the have conferences...

Will you be updating the site with your results? His arguments?

Yes I will, though it may be some time before we have the opportunity to do any of this...

 

[Alan McIntire]

If you're on a coast, watch distant vessels, and note that the masts of the vessels don't disappear below the horizon until after the rest of the ship has gone below the horizon. If you DON'T live near a coast, wait until the sun is setting on the horizon, about one solar width above the horizon . Telephone someone you know on the west coast, or better yet, overseas in England, or the Philippines, or wherever, and ask them how high above the horizon the sun is. Some of them are sure to say that the sun is BELOW the horizon. On a flat earth, the angle of the sun above the horizon could differ from place to place, but if it's below the horizon on ONE part of a flat earth, it's got to be below the horizon EVERYWHERE!

 

[Keith Mackie]

While not a classroom experiment, a great fun way to tackle the issue - you could even get the English teacher to join in - is to get a copy of Joshua Slocum's book 'Sailing alone around the world'. Slocum was the first man to sail single handed around the world back in the late 19th century and the book is an account of the voyage. It is a great read particularly at school level. The topic is rooted in the 'round earth' concept, effectively a grand experiment but also a lesson in geography. When he gets to South Africa he takes the train from Durban to Pretoria where he visits the president, Paul Kruger and gets into discussion over the 'flat earth' issue. I suspect that his account of this conversation, of how he 'teased' Kruger, made a significant contribution to the whole 'flat earth' movement.

 

[dennis_n]

An easy way I think would be to do a google call with another school at a different part of the world, then calculate the angle of the sun in the sky at the same time for both places. Obviously after doing some basic trigonometry, the results would only fit the round Earth model.