How do you give an example for finding net force?

--  6 people all trying to push a car out of snow

--  a Tug-o-War with 30 people of different sizes pulling on each end of the rope

--  you and your sister both pulling on the same doll (or Transformer)

--  lifting a book up from the table to a high shelf
    taking a book down from a high shelf to the table
    (one force is you; another force is gravity)

--  grabbing your big dog by his collar and trying to bring him inside

--  three people at the table all grab the ketchup bottle at the same time