How would Newton's second law apply to walking a dog?

Newton's
second law deals with the relationship between the force, mass, and acceleration of an object. 
When using Newton's second law you look at all the forces acting on an object, add them up, and
based on that determine the net force.  The net force, combined with the mass of the object will
determine the rate of acceleration.

When you are finding the net force there
are two possible conditions: first, the sum of all the forces could equal zero.  This means that
the forces are in balance. In the case of walking a dog, if you are walking at a constant speed,
that means that the force you are applying to the leash and the force the dog is applying to the
leash are equal and opposite.  So you...