Describe the forces on an object travelling at a constant speed?

If it is also traveling in a straight line, then either there is no force on it at all, or else all of the forces on it are 'balanced', that is, their vector sum is zero. If it is not traveling in a straight line, then a net centripetal force, in the direction of the center of curvature of its path, acts to bend its path, even though its speed isn't affected.