| She could 'understand' how she increased the force of her
| hand on the disk but couldn't really accept the inertia arguments about
how
| the disk increased its force back on the hand. 'Where does the disk get
the
| extra force when I push up with more force than its weight?' was her
| repeated question. - Rick Tarara
An intelligent question from this perspicacious student! You must refer
her to an understanding of the forces which hold the "rigid" body intact.
Show her graphs depicting the intermolecular force versus intermolecular
separation. Then show her that when she pushes on the object she forces its
surface molecules closer to their underlying neighbors (than the equilibrium
separation). This gives rise to an intermolecular repulsive force.