Why does a block of plastic released under water come up to the surface of water?

Given:

A block of plastic released under water comes up to the surface of the water.

To do:

To explain the reason why a block of plastic released under water come up to the surface of the water.

Solution

A block of plastic released under water comes up to the surface of the water. Let us find the possible reason why an object comes up to the surface or sinks-

Reason for coming up to the surface:

When an object is immersed in a fluid such as water, two force acts on the object.

1. Buoyant force by the water upwards

2. Weight of the body downwards

If the buoyant force is greater than the weight then the object will come up to the surface.

If the buoyant force is less than the weight, then the object will sink.

Conclusion:

From the above explanation, now we can conclude that a block of plastic released under water come up to the surface of the water because the weight of the block of plastic is not heavier than the weight of an equivalent volume of water. In other words, we can state that when a block of plastic is totally submerged in water, the upward buoyant force on it is more than the gravitational force on it downward. Consequently, the plastic block comes up to the surface of the water when it is released underwater.