I can't see why I'd be more likely to lose track if it was just one post, if it's split up there are distractions in between with other people posting on the topic, quotes tend to get lost when they get too long and so on, I must have skipped and forgotten half of the details and points of argument I've had on my mind during this exchange just because of this. So I'd prefer if it wasn't necessary to go step by step. I read books for fun, I think I can take one forum post - as long as it's concise, to the point and not by Sandokhan.
If you think that submerging an object in a measuring cup with fluid in it isn't descriptive of how much fluid an object displaces (!?) perhaps you could suggest another experiment?
I'm very interested in how pvc is special in this regard.
(density of polyvinyl chloride is well over 1 g/cm3, there is variance in products but generally it actually does sink)
Let me explain why it's important as to what you use and as to why a bucket isn't going to show you a true picture of displacement.
Ok, to start with, the iron sinks to the bottom of the bucket and obviously displaces the water.
The pvc won't sink so it won't displace as much. Now this is key, so keep this in mind as I move on.
Let's change the block to an iron block and a solid wood block of exactly the same size. Now you drop them in and they both fall to the bottom of the bucket and displace the same amount of water......but.....is that the whole story?
The answer is no. You see, the bottom of the bucket has stopped the objects from sinking any further because it's created a barrier. Now think about what I'm about to say, seriously.
To understand about mass and displacement in full you require super deep water to actually gauge displacement of water with any object.
For instance, let's get back to the iron and wooden block.
If you dropped them into a deep ocean, they would both sink....but, the iron block would continue to sink and the wooden block would stop sinking Why?
Because the wooden block still has trapped air inside of it and although the iron does, too, it's minute compared.
Because of this, it makes the wooden block more buoyant.
Now then, if we applied pressure to the wooden block to keep pushing it down to the same depth that the iron block was at, you would then see that it doesn't displace the same amount of water. Why?
Because it will be compressed into a smaller block by the pressure of the water, meaning the water will squeeze out the trapped air inside of it.
To give you an example of what I'm telling you is to look at a submarine.
Now imagine building a submarine out of solid iron, including inside of it. Basically a solid block in the shape of a sub.
Now you also have a normal sub of exact size, filled with the usual atmospheric pressure.
You drop them in the water and the solid one sinks but you have to force the other one down.
As you force it down, it will implode. Basically all of the air will be forced out and your sub will be a lot smaller and displacing a lot less water by this time.
On land it works similar, except you are measuring a mass that is subject to the amount of atmospheric pressure it can repel - or to put it in displacement terms, how much of that mass displaces the air it's in which is why I used the sponge and lead block to show you that absorbtion of atmospheric pressure will render the sponge lightweight when measured, as opposed to the lead block that will absorb very little, which is why it's so dense and why that density is measured on scales due to atmospheric pressure upon its mass.
To put it simply, measuring scales are simply denpressure scales, because that's what everything is and all that can be measured. It is not the actual object in itself, but what that object pushes against, which is atmospheric pressure and the ground. Put a measuring scale in between and that's what it weighs.