Since metal is more dense than water, how is it possible for a metal boat to flo
ID: 1998423 • Letter: S
Question
Since metal is more dense than water, how is it possible for a metal boat to float? Ocean-going ships in port are loaded to the so-called Plimsoll mark, which is a line indicating the maximum safe loading depth. However, in New Orleans, located at the mouth of the Mississippi River, where the water is brackish (partly salty and partly fresh), ships are loaded until the Plimsoll mark is somewhat below the waterline. Why? Lead has a greater density than iron, and both are denser than water. Is the buoyant force on a lead object greater than, less than, or equal to the buoyant force on an iron object of the same volume? Explain. An ice cube floats in a glass of water. As the ice melts, how does the level of the water in the glass change? Would it make any difference if the ice cube were hollow? Explain.Explanation / Answer
1. For floating the weight of the object must be equal to the buoyant force acting upward on the object. The buoyant force depends on density of the water displaced by the object as well as on the volume of the water it displaces. So the metal boat of having large surface area will displace large amount of the water. Hence buoyant force will be larger making it equal to the weight of the boat.
2. This is because the density of the salty water is more than the pure fresh water. So density of the water to be displaced is high which in turn will make the buoyant force high. Hence the ships are loaded in that way to counter balance the buoyant force.
3. Buoyant force will be equal for both iron and lead if the volumes are the same as it depends on the amount of the water displaced which in turn depends on the volume of the objects.
4. When ice cube floats on the water, most of the portion of the ice cube is already immersed in the water. So it will not make any rise in the water level even if it melts. The hollow ice cube will also take same volume in the water. So there will be no difference in the water level.