Originally Posted by alansmith
If the brick is hollow and made of plastic versus a brick of the same dimensions is made of gold...versus a brick that is same dimensions with sand inside of it....help me...
I'd say buoyancy is a pretty important concept
to get your head
around if you are going boating
. Get out your rubber ducky and hit the tub.
Since I'm not sure of the relative density of sand vs gold vs "plastic" I'll use an easier example: A bowling ball and a basketball. Imagine they are the same size. That means the are the same "volume", they take up the same amount of space. Lift
them up. That bowling ball is a lot heavier than the basket ball, yeah? Its more dense.
Throw the basketball in the tub. Look at the water level in the tub. It didn't change much, right? And the basketball is almost sitting on the surface of the water. It didn't displace, or relocate, very much water. It took very little water to equal the weight of the basketball. It didn't have much ability (weight) to lift
Now place the bowling ball in the tub. Check out how much the water level in the tub rose, now that the bowling ball is sitting at the bottom of the tub. The bowling ball displaced a volume of water equal to the bowling ball's volume, and that still didn't equal the weight of the bowling ball. Its more dense than water, so it sank.
From visualizing this, it should be clear that it is the density of the object itself, and not the material its made of, that determines whether something floats. A piece of glass sinks, its a denser material than water. But an empty beer
bottle floats, because the density of the bottle itself (its mass divided by the space the bottle takes up) is low. Splash around and fill that bottle with water though, and it'll sink, just like a swamped vessel. Once full of water, the density of the bottle (the mass divided by the space it takes up) has increased.