Question

Why does a needle made of iron sink in water but a hollow ship made of iron float on water,though the ship is much heavier than the needle?

Answer 1

1. The needle made of iron sinks in water because the mass of the water it displaces is less than the mass of the needle itself.
2. Thus the buoyant force acting on the needle is less than the weight of the needle, hence it sinks.
3. Ships are hollow and built so that, the mass of the water they displace is more than the mass of the ship itself.
4. Thus the buoyant force acting upwards on the ship is more than the weight of the ship, hence it floats.