Question

why in still water a submerged object does not move sideway​

Answer 1

All objects, even those that float, displace some water. Specifically, when placed in water, an object sinks into the water until it displaces an amount of water equal to its own mass. The more mass an object has, the further it sinks. A 1 g object will sink until it displaces 1 g of water.

Answer 2

Explanation:

When an object is immersed in a fluid, it feels lighter than when it is in the air. The surrounding fluid presses against the object from all directions. ... The upward and downward forces would not be the same because the fluid pressure increases with the depth.

hope it helps you