Why does an iron needle sink in water, but no an
iron ship
Answers
Answer:
Explanation:
In water, an iron needle sinks, but an iron ship floats. Archimedes's law states a body immersed in water displaces its volume of water. If this displaced volume of water weighs more than the body immersed, the body will float. If it weighs less than the body, the body will sink.
calculations with water are easy. Water weighs 1.0 tonnes per cubic metre. The density of steel is 7.8 tonnes per cubic meter. A solid ball of iron, whose volume is one cubic metre (radius 62 cm) weigs 7.8 tonnes. 7.8 is greater than 1.0, so the ball will sink. However, a steel boat whose weigh is one tonne is far greater by its volume than 1.0 cubic metres (it is likely it is at least 5 m long and has beam of 1.5 m or more), so its weight divided by its volume is far less than 1.0 tonnes/m^3The majority of the volume of a hollow boat is empty air, whose density (and weight) is negligible.
To put a long story short: anything with overall density (overall weight divided by overall volume) less than 1.0 will float, but those with greater than 1.0 will sink. This is why a solid plank of wood floats, but a solid ball of steel will sink.
However, the overall density of hollow objects (they are filled with air or vacuum) is far less than that of solid objects, as the vast majority of their volume is air or vacuum. This is why they float.
This applies also to aeroplanes only in water, but not in the air. An aeroplane will float on water (at least as long as it gets its fuselage to get filled with water - the air rushes out and water displaces it, increasing its weight dramatically until it sinks!) but not in the air. Oh, and floatplanes (which have hollow floats) and flying boats (which have hollow hulls) do indeed float. On water, not in the air.
Aeroplanes fly because their wings create lift. They essentially convert engine power into flight. Buoyancy is not the same as lift. An aeroplane wing creates lift by Bernoulli’s principle, and the greater the airspeed, the greater the lift as well. To fly, an aeroplane needs airspeed. An anchored ship will float, but a grounded aeroplane won’t fly.
The same law of Archimedes, however, applies to air as well: if the volume of the body immersed in the air weighs less than the displaced volume of air, it will float. This is the reason why we call aeroplanes as “heavier than air aircraft”.
There are indeed aircraft which are lighter than air. We call them airships. An airship has a humongous volume which is filled with gas which is less dense than air, so that the overall density of the airship is less than that of air. Airships and balloons are thus called “lighter than air aircraft” and the same principles apply to them as do on boats.
Answer:
Explanation:
the Iron needle is compact and its density is 7.6 g/cm3 Thus, as the density of iron needle is more than 1 g/cm3 therefore, it sinks in water. However, the iron ship is constructed in such a way that it is mostly hollow from within, thus, the volume of the iron ship becomes very large as compared to its mass and hence its density is less than lg/cm3 . As the density of iron ship is less than 1g/cm3, therefore it floats in water.