But you already know that because FG this is what the standards call the “weight” of the item, and for a given volume, weight depends only on density. If you throw these blocks into a lake, of course the styrofoam will float and the steel will sink. Apparently it has something to do with density.
What if you had a block of water with the same volume? If you could somehow hold this cube of water, it would feel quite hefty, about 62.4 pounds. If you place it carefully in a lake, will it sink or bounce on the surface like Styrofoam? Neither, right? It will just sit there.
Since it does not move up or down, the total force on the body of water must be zero. This means that there must be a force opposing gravity, pushing upwards with equal force. We call it buoyancyand for any object, the buoyant force is equal to the weight of the water it displaces.
So let’s think about this. The steel block displaces the same amount of water, so it has the same upward buoyant force as the water block. But because it is denser and has more mass, it falls.
Generally speaking, an object will sink if the force of gravity exceeds the force of buoyancy, and will float if the force of buoyancy exceeds the force of gravity. Another way to say it is that an object will sink if it is denser than water and will float if it is less dense.
And right in the middle, the object won’t sink or rise to the surface – this is called neutral buoyancy. Humans are almost neutral because our bodies are 60% water. That’s why you feel weightless under water – the force of buoyancy largely balances the force of gravity.
Avasta! Hang in there, buddy. Aircraft carriers are made of steel and weigh 100,000 tons, so why do this They platform? Can you guess? This is because of their shape. Unlike a block of steel, a ship’s hull is hollow and filled with air, giving it a gigantic volume relative to its weight.
What if you start filling it with cargo? The ship becomes heavier, which means it must displace more water to reach this balance point. Generally speaking, when you lower a boat or ship into the water, it will sink until the weight of the water it pushes out of the way equals the total weight of the boat.