The Cavendish Experiment

Awesome.

How did we ever learn anything before Youtube?

The public library… but I have to agree,… you tube or the internet as a whole, diffidently makes it easier…

OK, I'm impressed. I didn't think it was possible to do this with an "amateur setup". The coup de gras was the time lapse video.

Check BlueMarbleScience chanel in YouTube. He made this experiment and expalins the details very good.

Would this be accurate,… or how much would it be attributed to Foucault pendulum experiment.

it seems some what similar. Would be a great experiment on the ISS. Similar experiments they did is with some salt in a clear zip lock bag… it was determined that the attraction was static electricity. Not saying it’s the same.

..."Did someone perform the Cavendish experiment in outer space?

The great thing about space and spacecraft is that you can perform the Cavendish experiment on very grand and very finely tuned scales.

For example, OSIRIS-REx was recently orbiting a large lump of kitty litter known as 101955 Bennu. It was an excellent example of the Cavendish experiment: a lump of matter smaller than a large hill on Earth had enough gravity for an artificial probe to orbit it.

Henry Cavendish would be jealous that the experiment to measure the gravitational constant could be conducted in such an environment, free of aerodynamic drag, friction from pivots, and the like."....

https://www.quora.com/Did-someone-perform-the-Cavendish-experiment-in-outer-space

....…"Juno’s mission is to perform ultra-precise, accurate measures of Jupiter’s gravity from its different layers. Jupiter isn’t a simple ball of gas, it’s a complicated, layered planet with liquid and solid-ish layers. The different layers are measured by assessing Juno’s gravitational acceleration near Jupiter: the Cavendish experiment on one of the grandest of scales."...

...."The Cassini probe spent the last months of its life taking part in a Cavendish experiment. Astronomers have been very interested in the mass of Saturn’s rings. However, Saturn spins quickly and has a substantial equatorial bulge, which hindered Cassini’s attempts to measure the mass of the rings from outside the rings. So Cassini’s Grand Finale involved diving between Saturn and its rings and - in a test of gravity that would make Cavendish smile - measured how Saturn’s gravity pulled it one way while the rings pulled another."...

You've got a good point there. It wouldn't take much static charge on one or both of the moving or stationary weights to have the same effect.

It would be something that could be checked out. You can calculate the moment of inertia of the torsional pendulum and from the period of oscillation you could calculate the spring constant of the suspending wire and the torsional force as a function of position.

By filming the motion before and after the lead bricks were in place, you could measure position, velocity, and acceleration to compute total force. By subtracting off the torsional force to give net force and combining with distance, you could calculate calculate G.

It would be interesting to see how it compares to what Mr. Cavendish came up with.

Or maybe ground everything and run the experiment again.

Wouldn't any static charge be neutralized upon contact between the two...? ...but to me it seems any charges would have more than enough time to bleed off, this experiment takes place over many hours....

As you indicated in your first post, the time-lapse videos were quite revealing. It's pretty clear that one of the kilogram masses bounced off its lead brick, in spite of the low elasticity of lead.

Static electricity has nothing to do with the Foucault effect that Phoenix mentioned.

In any case, I'd have liked to see the bricks placed on the opposite sides of the torsion balance, although that would probably have taken longer than one Sunday...

By Foucault effect, I assume you mean the precession of a swinging pendulum caused by the earth's rotation.

I can see that a hanging torsion pendulum might maintain its orientation to the inertial frame, twisting as the earth rotates. But the addition of the stationary weights would have no effect on that, and the video clearly showed that the movement started when the stationary lead bricks were put into place.

I'm not saying a static charge was present, just that it should be ruled out.

Our high school physics teacher (more than 50 years ago) played a video of this experiment. As I recall the stationary masses were two large boxes filled with sand. The balanced weights (forget what they were) were suspended by a tape from a reel to reel tape recorder.

The experimenter in the film was an old physics professor. The set-up was very rough and ready. He used a couple of wooden boxes filled with sand, which he pushed into position after the suspended weights had found their position of rest. The tape from a reel to reel tape recorder was used to suspend the balanced weights - a long, very very weak torsion bar. The flats of the tape provided a visual indication of any twist, making it easier than a round wire to find the position of rest of the balanced weights. I found it to be an astonishing demonstration that you don't need the mass of a planet to produce a gravitational effect.

Thanks. Couldn't the bar be stopped from swinging before the lead bricks were applied?

Also C.V. Boys had a similar experiment (to measure G).

Well I would imagine the Moon is causing the noise, I guess you could neutralize the effect, but that might get a little complicated...

The period of the moon is a month. There is no reason to expect it to introduce noise in an experiment that only lasts a few hours, or even a couple of days.

I presume that the noise comes from such sources as imperfect position when the balance is first released, air currents, and the experimenter walking around.

The experimenter did an excellent job of balancing the weights, but it would take hours to determine the correct neutral position, and extremely careful hand movement to release the pendulum at that position.

There are nearly always ways to improve any experiment. My first suggestion would be to set up a system of cords and pulleys, perhaps with Teflon pads under the Lead blocks, so those blocks could be moved in or out together, without walking around.

Then what is causing the tides to shift from high to low every 6 hours...?

I guess you got me there, except that is due to the rotation of the Earth with respect to the Moon, and affects all parts of the pendulum proportionally, so should have virtually no effect on the rotation of the pendulum.

Anything that changes the period of rotation of the pendulum must exert a different horizontal force on one end of the pendulum arm than on the other end.

Getting nit-picky, one end of the pendulum arm will be closer to the moon than the other most of the time, but the effect of that on the rotation of the pendulum will be truly miniscule.

I think the Moon and/or Sun's gravity pulling from one end or the other, might cause an imbalance...but in any case there was some repeating pattern of imbalance occurring and it's effect was a known quantity, even if its source was not.....

Has anyone calculated the restoring torque from the suspension wire? I suspect it may be the cause of the rotational period of the meter stick and weights. It might take many hours for air resistance to stop it; if it could be stopped at mid-stroke, it should be at the neutral position. Then, addition of the lead bricks would cause it to move again. Forget the moon! Its effect on the torsional motion is probably negligible.

Has anyone calculated the restoring torque from the suspension wire?

The period of a torsional pendulum T=2pi x sqrt(I/k), where I is the moment of inertia and k is the spring constant (torque/radian). The moment of inertia can be calculated as the sum of masses x square of distance from axis. Given T and I, you can solve for k.

https://pressbooks.online.ucf.edu/osuniversityphysics/chapter/15-4-pendulums/#:~:text=The%20period%20of%20a%20torsional,and%20torsion%20constant%20are%20known.

The earth and moon revolve around the center of gravity of the earth-moon system. The ocean tide is high both on the side closest to the moon and the side farthest from the moon.

On the closest side to the moon, the moon's pull is stronger than at the center of gravity, raising the tide. On the farthest side, the moon's gravity is weaker, so centrifugal force raises it there.

And when you remember that there are people that think the Earth is flat and gravity isn`t exist, but this is density and buoyancy, you can facepalm!

For anyone interested, how to determine G ( = 6.674*10⁻¹¹ m³/kg-s² ), the gravitational constant:

https://www.school-for-champions.com/science/gravitation_cavendish_experiment.htm