Question

why do some things sink?

the weight of the body applies downward force on the water molecules
and according to newton's 3rd law of motion there is a equal opposite reaction force
so the both get balanced out so now the only force acting on the object is the upthrust so there's no downward force so why do some things sink?

Answer 1

The object which is more dense than the fluid sinks in that fluid.

This is related to Archimedes principle.

Explanation:

When a body is placed in a fluid then it experiences Buoyant force

due to the fluid which is equal to the weight of fluid displaced by it.

If the weight of the object is larger than the buoyant force then the

object sinks in that fluid.

The buoyant force on the object is given by `F`

`F = V_b.D_f.g`

where :-

`1) V_b` is the Volume of body inside the fluid.

`2) D_f` is the Density of that fluid.

`3)` `g` is the acceleration due to gravity.