Define upthrust and state its S.I. unit.

Hint:In upthrust, the body feels an upward force just opposite to the path of the body. Explain properly the term “upthrust” and then write its S.I. unit. Upthrust is actually the buoyant force or we can say that buoyant force and the upthrust are the same. So, both these terms will have the same S.I. unit.

Complete step by step answer:Upthrust is defined as the upward force exerted on a solid body when it is submerged in a fluid for example water completely or partially. Here, the weight of the fluid (water) is equal to the weight of the fluid displaced by the water.
Weight is a force that acts at all times on all objects near Earth. Thus, weight is the other name of force in physics. When an object is immersed in water then the pressure exerted by the fluid on the object is known as buoyancy. And the force exerted by the object is upward force. Therefore, when the depth of the fluid (water) increases then the pressure also increases. Upthrust force is the same as the buoyant force. Hence both the terms will have the same S.I. unit.
The S.I. The unit of buoyant force is Newton (represented by ${\text{N}}$).

Thus, the S.I. The unit of upthrust force is also Newton (${\text{N}}$).

Note:If an object having density greater than that of the fluid in which it is submerged then the object tends to sink. If the object is either less dense than the liquid or is shaped then the object doesn’t sink. Or we can say that, if the relative density of a substance is less than one it floats in water and substances with a relative density greater than 1 then it will sink in water.