Consider two identical small steel balls dropped into two identical containers, one filled with water and the other with oil. Which ball will reach the bottom of the container first? Why?

When a body is moving in a liquid, it experiences a backward dragging force. this backward dragging force is given by the formula

F = 6 π η r v

where, η is called the coefficient of viscosity, r be the radius, v be the velocity of object.

As we know that the coefficient of friction for oil is more than water so the dragging force in oil is more than water.

So, the balls in water comes first.