  Modified Newtonian dynamics can be considered as an effect derived from a
squeezable extra dimension space. The third law of Newtonian dynamics can be
managed to remain valid in the 5-space. The critical acceleration parameter
$a_0$ appears naturally as the bulk acceleration that has to do with the
expanding universe in this setup. A simple toy model is presented in this
Letter to show that consistent theory can be built with the help of the extra
dimensional space.
