I don't know what kind of real situation you are talking about, so I can only give a rough answer here:
First, let's clarify a theorem: the buoyant force on a object. is equal to the gravity of the liquid it displaces.
Second, understand that the density of liquids changes with temperature and the volume of objects also changes with temperature.
For example, the thrust force exerted on iron in water at 90 degrees Celsius is equal to the density of water at 90 degrees * volume displaced, and the thrust force exerted on the iron in water at 4 degrees Celsius is equal to the minimum density at 4 degrees* of open volume displacement, the results obtained are of course different.
Also, if it's a small piece of iron floating on water, that's different. Due to the surface tension of water, sometimes objects with a density greater than that of water can float on water. GivenAlthough temperature affects surface tension, the buoyant force is sometimes equal to the gravity of the object, and sometimes it is equal to the gravity of the water being displaced.
I'm not an expert and my answer is sloppy, but I still hope it can help you.
Use a balance and a beaker to weigh an appropriate amount of water with a mass of m1, and pour it into the large test tube
② Take an appropriate amount of sand and put it put it in a small test tube and use a balance to weigh the total mass m2, such that m2>m1
③ Put the small test tube containing sand into the large test tube and observe whether the small test is obtained. the tube floats. If the small test tube does not float, the amount of water and sand should be adjusted under guaranteed conditions to make the small test tube float in the large test tube.