  Shear flows have been prescribed in numerical models of coronal mass
ejections and flares for decades as a way of energizing magnetic fields to
erupt. While such shear flows have long been observed in the solar atmosphere,
until recently, there was no compelling physical explanation for them. This
paper will discuss the discovery that such shear flows are readily explained as
a response to the Lorentz force that naturally occurs as bipolar magnetic
fields emerge and expand in a gravitationally stratified atmosphere. It will be
shown that shearing motions transport axial flux, and magnetic energy from the
submerged portion of the field to the expanding portion, strongly coupling the
solar interior to the corona. This physical process explains active region
shear flows and why the magnetic field is found to be nearly parallel to
photospheric polarity inversion lines where prominences form. Finally, shear
flows driven by the Lorentz force are shown to produce a loss of equilibrium
and eruption in magnetic arcades and flux ropes offering a convincing
explanation for CMEs and flares.
