What is the drag force, buoyancy force, and gravitation force on a grain in motion?

Drag Force - A drag force is a force of friction caused by a body's movement through fluid like water, air etc.

Buoyancy force - Buoyancy or upthrust force is an upward directed force imposed by a fluid opposing an object's weight

Gravitation force - Gravitational force is a force of attraction that draws mass from any object.

Explanation:

Drag Force - A drag force is a force of friction caused by a body's movement through fluid like water, air etc. Drag force functions contrary to direction of the current flow speed

Buoyancy force - Buoyancy or upthrust force is an upward directed force imposed by a fluid opposing an object's weight. Due to weight of the fluid, pressure rises with depth in a section of fluid.

Gravitation force - Gravitational force is a force of attraction that draws mass from any object.