[nickrulercreator]

In Chapter III - THE EARTH NO AXIAL OR ORBITAL MOTION., Rowbotham proposes an experiment to test if the Earth is rotating. It goes like this:

Picture a ball on a ship. If you drop the ball from the top of the mast, and the ship is stationary, the ball will fall straight down. If the ship is in motion and you drop the ball, then the ball, relative to the mast, will still drop straight down. This is a result of the ball's momentum given to it by the ship. He relates this to the different models of the Earth. If the Earth was stationary and you dropped a ball, the ball will go straight down, and the same for a rotating Earth.

Rowbotham then proposes that to test whether Earth rotates, you must throw a ball straight up while the ship is in motion. He gives us this image:

His text goes as is:

put the ship in motion, and let the ball be thrown upwards. It will, as in the first instance, partake of the two motions--the upward or vertical, A, C, and the horizontal, A, B, as shown in fig. 47; but because the two motions act conjointly, the ball will take the diagonal direction, A, D. By the time the ball has arrived at D, the ship will have reached the position, 13; and now, as the two forces will have been expended, the ball will begin to fall, by the force of gravity alone, in the vertical direction, D, B, H; but during its fall towards H, the ship will have passed on to the position S, leaving the ball at H, a given distance behind it.

Rowbotham then says that, because when we throw a ball into the air while standing on Earth's surface, and it does not stop at its peak altitude, this means Earth's surface is not moving under the ball, and thus it is stationary.

This makes no sense. What would cause the ball to lose all horizontal velocity at D? Why would the ball not continue in the horizontal direction as it falls, just as it moved in the horizontal direction as it rose? In real life, if you threw the ball upward while the ship was in motion, it would travel in a vertical line relative to the ship. It would not stop at its maximum altitude, like Rowbotham claims. That's pure nonsense.

This doesn't prove the Earth is flat or round, it just proves Rowbotham was very wrong in his experiment.

[Pete Svarrior]

Yes, unless we're both missing the same thing, that does appear to be a particularly egregious misunderstanding of classical mechanics.

I mean, if the experiment were to be performed, we would indeed most likely see the ball lag behind the ship to some extent due to drag, but that's obviously not transferable to the scenario of the rotating round Earth.

In short, I agree that the triangular trajectory is nonsense - it should be a parabola, although it could still illustrate the point he's trying to make when corrected. Nonetheless, his point would still not be applicable here, and the experiment would not be conclusive.

[Rama Set]

One should not trust Rowbotham’s experiments as a general rule. They have pretty much all been shown to be badly conceived and/or executed.

[HorstFue]

Yes, unless we're both missing the same thing, that does appear to be a particularly egregious misunderstanding of classical mechanics.

If there anyone appears, to have a "particularly egregious misunderstanding of classical mechanics" than it's Mr. R..

I mean, if the experiment were to be performed, we would indeed most likely see the ball lag behind the ship to some extent due to drag, but that's obviously not transferable to the scenario of the rotating round Earth.

Momentum conservation: The ball initially has the same horizontal speed as the ship. This monument and thus the horizontal speed of the ball does not change, unless some other force would be applied to the ball. I see non, unless some tiny air friction.
As the ball has the same horizontal speed as the ship (and the ship does not change speed), it will always be exactly above the point, where it had been thrown vertically up in the air and when it comes down will nearly hit the same point.

The interesting thing is, that R. even described a separate "experiment" for that part, where the ball goes down again. And came to the conclusion, that ship's motion is not relevant:

IF a ball is allowed to drop from the mast-head of a ship at rest, it will strike the deck at the foot of the mast. If the same experiment is tried with a ship in motion, the same result will follow

In short, I agree that the triangular trajectory is nonsense - it should be a parabola, although it could still illustrate the point he's trying to make when corrected. Nonetheless, his point would still not be applicable here, and the experiment would not be conclusive.

If R. paints the course of the ball as a straight line, than "the triangular trajectory is nonsense - it should be a parabola" is another hint, that R. does not understand classical mechanics.

Nevertheless I agree, that this experiment does not proof anything.

[Tom Bishop]

Rowbotham is describing movement between points in space in his text and the illustrator from the book company, George Davies, drew lines between the points described. Rowbotham didn't draw that. Are you next going to tell us that Rowbotham is invalid because the illustrator drew the Round Earth more curvy than it is in some of the other illustrations?

The chapter has nothing to do with parabolic motion. Read: Nothing to do with it! It is not a tutorial on parabolic motion.

Also, where does it say in the chapter whether the ship is accelerating or moving at a constant speed?

[Rama Set]

Rowbotham is describing movement between points in space in his text and the illustrator from the book company drew lines between the points. Rowbotham didn't draw that. Are you next going to tell us that Rowbotham is invalid because the illustrator drew the Round Earth more curvy than it really is in other illustrations?

The chapter has nothing to do with parabolic motion. Read: Nothing to do with it! It is not a tutorial on parabolic motion.

Also, where does it say in the chapter whether the ship is accelerating or moving at a constant speed.

What a nice cop-out, “I know it’s Rowbotham’s book, and he almost certainly had final say on the illustrations, but it’s not his fault!”

Tom literally thinks Rowbotham is perfect.

[Tom Bishop]

You apparently have never worked in a group project before. Interpretations don't always click, and you can't always make your coworkers re-do everything.

It is easily argued by the publisher that the lines between the points was good enough and parabolic motion complicates things. If Rowbotham objects and the illustrator puts this in the book:



Then Rowbotham has to rewrite everything and explain what it is. A pointless exercise, considering the matter had nothing to do with what was being described. The publisher can easily veto pointless rewrites like that. There are such a thing as deadlines and budgets. The publisher is the one who is paying the illustrator, not Rowbotham.

[edby]

You apparently have never worked in a group project before. Interpretations don't always click, and you can't always make your coworkers re-do everything.

It is easily argued by the publisher that the lines between the points was good enough and parabolic motion complicates things. If Rowbotham objects and the illustrator puts this in the book:



Then Rowbotham has to rewrite everything and explain what it is. A pointless exercise, considering the matter had nothing to do with what was being described. The publisher can easily veto pointless rewrites like that. There are such a thing as deadlines and budgets. The publisher is the one who is paying the illustrator, not Rowbotham.

So you are saying R's argument would be perfectly valid, had he drawn a parabola instead of a triangle? But isn't the argument invalid under classical mechanics anyway? Classical mechanics says you cannot distinguish between a moving surface and a stationary one simply by throwing objects in the air.

[Ofcourseitsnotflat]

If anyone wants to see this demonstrated, just look at the opening scene of the first episode of Young Sheldon.

Replace ship with model train. One carriage contains a vertical air-driven firing tube to fire a ball upward. Device fires ball up before train enters model tunnel. Ball continues moving at same rate as train, moves over tunnel as train moves under, and drops back into firing tube as train exits tunnel. The ball is not left behind by the train.

I would post a video if I could, but copyright seems to be preventing any appearances on YouTube or suchlike.

[Tom Bishop]

To the above posts:

Where does it say that the ship was moving at a constant speed?

From what I can see the ship was stationary and then put into motion; it accelerated. You are reading what you want to read.

[Ofcourseitsnotflat]

Also, where does it say in the chapter whether the ship is accelerating or moving at a constant speed?

The text says "put the ship in motion", doesn't it?

Well, there's three alternatives;
Ship at constant speed
Ship accelerating (speeding up)
Ship decelerating (slowing down)

You appear to suggest neither of the first two apply; are you explicitly saying the ship was slowing down? Or are you merely accepting that the conditions of the experiment are badly or unclearly stated?

[Tom Bishop]

Rowbotham is talking about acceleration. The ship is accelerating, and leaves the ball behind. The same happens with the next example.

The same result will be observed on throwing a ball upwards from a railway carriage, when in rapid motion, as shown in the following diagram, fig. 48. While the carriage or tender passes


FIG. 48.

from A to B, the ball thrown upwards, from A towards (2, will reach the position D; but during the time of its fall from D to B, the carriage will have advanced to S, leaving the ball behind at B, as in the case of the ship in the last experiment.

Look at the spacing of the trains. Accelerating. The ball is left behind. True.

The illustrator also made it look like the ball hit the train again, but if you read the text it is clearly conveyed what Rowbotham is describing.

[Rama Set]

You apparently have never worked in a group project before. Interpretations don't always click, and you can't always make your coworkers re-do everything.

The illustrator was a co-worker? Or an employee? How do you even know?Either way, it’s very shoddy to put out a technical drawing that doesn’t describe what you want. It’s even worse if you don’t realize the drawing doesn’t describe what you want. Take your pick. 

[Ofcourseitsnotflat]

If anyone wants to see this demonstrated, just look at the opening scene of the first episode of Young Sheldon.

...  I would post a video if I could, but copyright seems to be preventing any appearances on YouTube or suchlike.

Found it. At 1min3secs approx

[Ofcourseitsnotflat]

The ship is accelerating, and leaves the ball behind. The same happens with the next example.

The same result will be observed on throwing a ball upwards from a railway carriage, when in rapid motion

But there's no mention of acceleration in the text, just "motion" or "rapid motion" ... and no indication that the spacing between trains indicates differing rates of motion between them.

The spacing between ships, IF this is taken as an indicator, would seem to show the ship slowing down, wouldn't it?

[edby]

Rowbotham is talking about acceleration.

(1) Rowbotham uses the term ‘rapid motion’, not ‘acceleration’. These have a different meaning. And (2) if he did mean acceleration, his argument would be valid only if the earth had an angular acceleration. Is that what Rowbotham’s argument is aimed against, i.e. an accelerating earth? Where does he say this?

[Tom Bishop]

Rowbotham is talking about acceleration.

(1) Rowbotham uses the term ‘rapid motion’, not ‘acceleration’. These have a different meaning. And (2) if he did mean acceleration, his argument would be valid only if the earth had an angular acceleration. Is that what Rowbotham’s argument is aimed against, i.e. an accelerating earth? Where does he say this?

Rotating bodies do exhibit acceleration on the surface.

[edby]

The juggler standing in the ring, on the solid ground, throws his balls as vertically as he can, and they return to his hand; but when on the back of a rapidly-moving horse, he should throw the balls vertically, before they fell back to his hands, the horse would have taken him in advance, and the whole would drop to the ground behind him.

He does not say the horse is accelerating.

Had there been motion in the direction from west to east, and at the rate of 600 miles per hour (the supposed velocity in the latitude of England), the result would have been as shown in fig. 49.

He says ‘600 miles per hour’ and ‘velocity’, not ‘acceleration’. This is where he argues that if the earth were moving, a cannon ball fired absolutely vertically in the air, would land somewhat behind the mouth of the cannon. He seems not to have understood momentum.

[edby]

Rowbotham is talking about acceleration.

(1) Rowbotham uses the term ‘rapid motion’, not ‘acceleration’. These have a different meaning. And (2) if he did mean acceleration, his argument would be valid only if the earth had an angular acceleration. Is that what Rowbotham’s argument is aimed against, i.e. an accelerating earth? Where does he say this?

Rotating bodies do exhibit acceleration on the surface.

This is entirely incorrect, unless there is angular acceleration. But there is no angular acceleration of the earth. It rotates at a constant angular velocity.

[Tom Bishop]

Rowbotham is talking about acceleration.

(1) Rowbotham uses the term ‘rapid motion’, not ‘acceleration’. These have a different meaning. And (2) if he did mean acceleration, his argument would be valid only if the earth had an angular acceleration. Is that what Rowbotham’s argument is aimed against, i.e. an accelerating earth? Where does he say this?

Rotating bodies do exhibit acceleration on the surface.

This is entirely incorrect, unless there is angular acceleration.

Get onto a merry-go-round that is rotating at a 'constant speed' and see if you can throw a ball up straight into the air and get it to fall back into its same position with you.