Forces Acted on Objects Immersed in Liquid

In order to solve the problem related to object immerse in water, it's important to know the all forces acted on the object.

Case 1:

1. The density of the object is lower than the density of the liquid. The object floats on the surface of the water.
2. The forces acting on the object is
1. the weight of the object(W)
2. the upthrust (F)

Forces are in equilibrium, hence

F = W

Case 2:

1. The density of the object is greater than the density of the liquid. The object sink to the bottom of the water.
2. Lying on the bottom of the water, there is a normal reaction acted on the object.
3. The forces acting on the object is
1. the weight of the object(W)
2. the upthrust (F)
3. Normal reaction (R)

Forces are in equilibrium, hence

F + R = W

Case 3:

1. The density of the object is greater than the density of the liquid. The object is hold by a string so that it does not sink deeper into the water.
2. The forces acting on the object is
1. the weight of the object(W)
2. the upthrust (F)
3. Tension of the string (T)

Forces are in equilibrium, hence

F + T = W

Case 4:

1. The density of the object is lower than the density of the liquid. The object is hold by a string so that it does not move up to the surface of the water.
2. The forces acting on the object is
1. the weight of the object(W)
2. the upthrust (F)
3. Tension of the string (T)

Forces are in equilibrium, hence

F = W + T