Free fall is commonly discussed as an example of the equivalence principle, in the context of a
homogeneous gravitational field, which is a reasonable approximation for small test masses falling
moderate distances. Newton’s law of gravity provides a generalisation to larger distances, and also
brings in an inhomogeneity in the gravitational field. In addition, Newton’s third law of action and
reaction causes the Earth to accelerate towards the falling object, bringing in a mass dependence in
the time required for an object to reach ground—in spite of the equivalence between inertial and
gravitational mass. These aspects are rarely discussed in textbooks when the motion of everyday
objects are discussed. Although these effects are extremely small, it may still be important for
teachers to make assumptions and approximations explicit, to be aware of small corrections, and also
to be prepared to estimate their size. Even if the corrections are not part of regular teaching,
some stu…