Question

The weight of the body applies downward force on the water molecules and according to Newton's third law of motion there is an 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 downward force so why do some things sink?

Answer 1

Hint : Use the Archimedes Principle to your advantage. When a body is immersed in it or positioned on its surface, the liquid exerts a force. This upward force is the resultant force. If the density of an object is greater than the density of liquid, it sinks. This is because an object's weight is greater than the buoyant force acting on it.

Complete Step By Step Answer:
If the object's density is higher than the density of the liquid, the object sinks into the liquid; if the object's density is less than the density of the liquid, the object floats on the liquid's surface. This occurs because when a body is submerged in water, the liquid exerts a buoyant force on it.
According to the Archimedes Principle, the upward buoyant applied force on a body immersed in a fluid, whether partly or completely submerged, is equal to the weight of the fluid that the body displaces and behaves in an upward direction at the displaced fluid's centre of mass.
This upward buoyant force is called thrust. When we reach a swimming pool or a river to swim, we experience a sense of weightlessness, which is caused by the water's thrust.

Note :
If the density of the object is less than or equal to the density of the liquid, the object will float. This is due to the buoyant force acting on the object's weight. Our weight is determined by the fluid in our environment. We feel different weights in a pool, river, or other body of water than we do on land (surrounded by air). This apparent weight is caused by the buoyant force.