Newton's 3 laws are all based around some form of motion and each plays a part in how the giraffe's head swings and what force it creates when striking a rival. Newton's second law, or the Law of Acceleration and Force, gives the best explanation of how a much larger head can be beneficial when creating force.
Newton's second law explains that Force generated depends on two inputs or variables, the acceleration of the object and the mass of the object. This relationship can be expressed with the equation force equals mass multiplied by acceleration, or:
In this equation both acceleration and mass are directly proportional to the force; increase either amount and the force will also increase. If a giraffe has a larger head than another giraffe supposedly the larger head would carry more mass and thus be able to create a larger force. If giraffes decide on a social order based around who could hit each other harder with their head, whichever giraffe had a larger head would already have an advantage due to the higher forces it could create.