So one thing I have seen on here is the idea that gravity isn't actually a thing, and that instead buoyancy, and so by extension density, is what causes objects to fall down, now there is a couple of flaws in this model but I am not here to debate those. Instead I have written an experiment you can do yourself from home that will disprove this model of Gravity. I have tested it myself, so I know it works, but the most important thing is that believers test it so they know in themselves that it works.
So what you do is you take two of the same bottle (any object will do, but water/any liquid makes it a bit easier) Now fill one bottle up with water and leave one empty.
Density is the mass of the object over the volume of the object, so with this experiment both bottles will have the same volume as they are the same bottle, but the filled bottle should be around an extra 0.5kg heavier due to the liquid this means it will have a a larger density.
So by the density model of Gravity, the heavier one should fall first as it has a higher density, now what you do is you hold them up as high as you can in the same orientation (as a control) and then you drop them. They should both hit the ground at the same time assuming you let go of them at the same time.
Human error will be the biggest cause for failure in this experiment as you could let go of one faster than the other so to get an accurate result, some kind of simultaneous release system could be built and a high speed camera can record the landing.
Note, I have chosen to use two of the same object as that will lessen the effect drag has since using an object with a larger surface area would cause more drag meaning that it would hit later (not a problem in a vacuum chamber)
So if anyone wants to do this experiment, I would be interested in seeing your results.
Also, the value for the acceleration due to gravity can be worked out using the equation
2s/t˛
Where S is the distance from the top to the bottom, and t˛ is the time taken squared.
This value should come out close to 9.81m/s˛