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Offline Regicide

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Let's do a Cavendish Experiment
« on: January 21, 2021, 02:57:10 PM »
Flat Earthers and Round Earthers seem to disagree on a few points. One of these is gravity, which is essential for Round Earth Theory and anethema to Flat Earth Theory... or at least the current one. Luckily, there is quite a simple way to measure gravity: The Cavendish Experiment. There are a few videos of Cavendish experiments available, mostly performed by teachers in less than perfect environments. So, rather than performing a simple experiment and then dissolving into disagreement over fine points, let's come to a consensus on how to perform a controlled Cavendish experiment and then execute that plan. Let's please keep this on topic and civil: this is an investigation, not a debate. I'll list all of the things I can think of to control:

Air currents: With the weak forces experienced by the objects in a Cavendish experiment, any outside perturbation is enough to disturb a system. Thus, it is best to control air currents, either by performing the experiment in a vacuum, or if that proves impractical, testing a control with objects of the same shape but a lower mass.

Magnetism: The test needs to be performed with weights which do not experience magnetism, and for that matter won't exude a static charge either.

Place of rest needs to be found.: The original Cavendish experiment was performed not to prove the existence of gravity, although gravity is needed for it to work. Rather, it was performed to find the gravitational constant, which it did so with remarkable accuracy. It did this by suspending the weights from a long wire, and allowing them to rotate. This of course twisted the wire, which introduced a torsion force into the system. By finding how far the weights are from the height of equilibrium when they come to rest, a gravitational force can be found. The best way in my mind to perform this would be to place a digital dial gauge under the beam and allowing the beam to spin back and forth without external weights. The lowest height it reaches should be the place of rest.


With all these in mind, I'll do the first procedure writeup, which will doubtless be modified.

1. Suspend a wire (exact length, gauge, and material TBD) from the ceiling (Could be performed in a large empty space, such as an empty gymnasium to minimize outside gravitational influences, or could be performed in a vacuum chamber if it's practical.
2. On the end of the wire, attach a beam (properties TBD) and to either side attach a weight of mass (TBD). Allow the system to rest for one hour.
3. Place a digital dial gauge under the beam so that it is measuring the height of the beam, and rotate the beam 90 degrees without allowing the wire to swing. Release and plot the height over the next (length of time TBD).
4. With the equilibrium height established, allow the system to come to rest at equilibrium. Place two empty containers of volume (TBD) (TBD m/cm) away, on scales of which the mass is already known. Wait one hour and measure the change in height of the beam.
5. Fill the containers with (material of extremely high density: lead, stone, etc.), so that the mass of each container is (TBD). Wait until the system reaches equilibrium and measure the height.
6. Remove the containers and allow the system to return to equilibrium.

If the height with the high mass containers is different to the equilibrium height without containers, then gravity exists.

Let's do this.
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Offline Pete Svarrior

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Re: Let's do a Cavendish Experiment
« Reply #1 on: January 21, 2021, 04:45:32 PM »
Since you seem interested, I would like to revive my Banana Challenge. Since the hypothetical effect of gravitation is supposed to affect all mass, I would like to see the experiment performed on bananas.

I'm also not convinced that you've described the Cavendish Experiment above. You talk about measuring heights (unclear how you propose they would change), which is not part of the experiment. A standard Cavendish setup looks something along these lines:



You will also want to understand why FE'ers don't consider the Cavendish Experiment to be particularly useful for the purpose you propose it for: https://wiki.tfes.org/Cavendish_Experiment
« Last Edit: January 21, 2021, 05:08:40 PM by Pete Svarrior »
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Offline Regicide

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Re: Let's do a Cavendish Experiment
« Reply #2 on: January 21, 2021, 08:36:56 PM »
The Banana Challenge is a hilarious idea, some of the responses seem to miss the point. The effect of gravity is indeed supposed to move all objects, proportional to mass and distance. I'll start with a thought experiment. According to the FDA, the average banana weighs 120 grams. So, let us place two 120 gram bananas a centimeter apart and calculate the gravitational force. I could calculate it myself, or I could usehttps://www.omnicalculator.com/physics/gravitational-force. Using the calculator, we can find that two bananas with center of mass 1 cm apart have a gravitational force of 9.611 × 10^-9 N, or a 9th of the force that a hydrogen nucleus exerts on it's electron. Oh dear. So bananas really don't attract each other very much. However, you asked me to demonstrate gravity, so I'll persevere. Assume a 1000 kg banana. When two of these are positioned with the centers one cm apart, the force of gravity is 0.66743 N, or around the force it takes to depress a key on a keyboard. So then, sir, you ask me to demonstrate gravity with bananas? Give me a couple of one ton bananas, then we can talk.

Anyways, the whole point of this thread is for Flat Earthers and Round Earthers to come to a consensus on a workable Cavendish Experiment, so I'll modify the writeup.

1. Suspend a wire (exact length, gauge, and material TBD) from the ceiling (Could be performed in a large empty space, such as an empty gymnasium to minimize outside gravitational influences, or could be performed in a vacuum chamber if it's practical.
2. On the end of the wire, attach a beam (properties TBD) and to either side attach a weight of mass (TBD). Allow the system to rest for one hour.
3. Place a digital dial gauge under the beam so that it is measuring the height of the beam, and rotate the beam 90 degrees without allowing the wire to swing. Release and plot the height over the next (length of time TBD).
    Attach a mirror to the beam, and using a laser, establish the angle of deflection. Allow the system to come to equilibrium, and record the angle.
4. Place two empty containers of volume (TBD) (TBD m/cm) away, on scales of which the mass is already known. Wait one hour and measure the change in height angle of the beam.
5. Fill the containers with (material of extremely high density: lead, stone, etc.), so that the mass of each container is (TBD). Wait until the system reaches equilibrium and measure the height angle.
6. Remove the containers and allow the system to return to equilibrium.

Looking forward to further collaboration!
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Offline JSS

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Re: Let's do a Cavendish Experiment
« Reply #3 on: January 21, 2021, 09:44:41 PM »
If you just want to show that mass is attracted to mass you won't need the mirror and laser.  With heavy enough weights the motion will be obviously apparent as they are attracted to each other.  You just need a camera to record the natural motion and then the change with the weights are added.

I don't think anyone here is going to be able to set up anything accurate enough to measure G, but the beauty of the Cavendish Experiment is even with a basic setup you can show that mass attracts mass. Measuring the force with precision takes a lot of work and setup and cost.  I doubt anyone here is going to go that far.

I might try the attraction part of this experiment though, I'll have to see what the densest materials I have on hand are. I have a large basement, so movement of the floor won't be an issue, but air currents always are an issue.

This is a good experiment to try as it's not an extreme amount of work or money and makes for a great demonstration.

It's rather pointless to expect it to change any minds however. As Pete demonstrated with posting the Wiki link, Flat Earthers seem to reject the very idea that the experiment is showing the effects of gravity, so doing it themselves won't help.

It's still worth doing and I may try and post my results here when I get around to it.  A good distraction from COVID quarantine at least.

Online SteelyBob

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Re: Let's do a Cavendish Experiment
« Reply #4 on: January 21, 2021, 09:48:22 PM »
You will also want to understand why FE'ers don't consider the Cavendish Experiment to be particularly useful for the purpose you propose it for: https://wiki.tfes.org/Cavendish_Experiment

The wiki article on Cavendish, and the broader challenges of measuring G, is a bit misleading tbh.

Quote
As suggested by the references above; until physics is able to isolate the gravitational interaction between laboratory masses to the point where other disturbing forces do not dominate the measurement, the Cavendish Experiment should be regarded for what it is: An inconsistent experiment which is admittedly disturbed and dominated by unknown or unmitigated effects, and which might or might not include "gravity" in the results seen.
 

The Cavendish methodology isn't the only show in town, for a start - which the article itself acknowledges, although it seems to use Cavendish as a catch-all for every technique. Second, the disturbing forces don't dominate, as such, but they do make getting precision results challenging. The wiki article itself describes a 450ppm deviation between results, and later on a 0.15% between results from different methods - we're into the third or even fourth decimal place before we see a difference. Talk of results billions of times less accurate than other universal constants sounds terrible, but it merely reflects how accurately we know other things.

It is an enormous and illogical leap to go from 'we can only measure it accurately to two or three decimal places' to 'it isn't real'. If different experimenters, using different techniques in different labs, are measuring G to be 6.67 × 10-11 Nkg-2 m2, and gravity isn't real, then what exactly are they all measuring? It ain't the same gust of wind or earth tremor, is it?

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Offline Regicide

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Re: Let's do a Cavendish Experiment
« Reply #5 on: January 22, 2021, 02:25:59 PM »
Sounds good JSS, a few considerations to be had just to shoot down complaints before they arise:

Obviously, stay away from objects that have magnetic forces.

Try to eliminate as many sources of heat and motion as possible, which includes yourself: set up a camera and leave the room.

Try it first with fake weights to account for air currents without a gravitational effect.

Even if the weights don't collide, that's to be expected: the experiment was originally designed so that the point where the torsion force counteracts the rotation can be measured.

Wait. The acceleration of a 100 kg weight and a 10 kg weight 1 centimeter apart is about 0.24027 meters per hour squared: be patient.

Looking forwards to seeing your results!
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Offline stack

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Re: Let's do a Cavendish Experiment
« Reply #6 on: January 22, 2021, 10:02:12 PM »
Sounds good JSS, a few considerations to be had just to shoot down complaints before they arise:

Obviously, stay away from objects that have magnetic forces.

Try to eliminate as many sources of heat and motion as possible, which includes yourself: set up a camera and leave the room.

Try it first with fake weights to account for air currents without a gravitational effect.

Even if the weights don't collide, that's to be expected: the experiment was originally designed so that the point where the torsion force counteracts the rotation can be measured.

Wait. The acceleration of a 100 kg weight and a 10 kg weight 1 centimeter apart is about 0.24027 meters per hour squared: be patient.

Looking forwards to seeing your results!

And don't forget to do it both ways. To see the opposite rotation/attraction under the same circumstances. As I'm sure everyone is aware, there are a bunch of DIY classroom/garage vid examples out there to help with set-up.