Suppose an electric current I flows along a magnetic flux tube that has poloidal flux and radius aϭa (z), where z is the axial position along the flux tube. This current creates a toroidal magnetic field B . It is shown that, in such a case, nonlinear, nonconservative JϫB forces accelerate plasma axially from regions of small a to regions of large a and that this acceleration is proportional to ץI 2 /ץz. Thus, if a current-carrying flux tube is bulged at, say, zϭ0 and constricted at, say, z ϭϮh, then plasma will be accelerated from zϭϮh towards zϭ0 resulting in a situation similar to two water jets pointed at each other. The ingested plasma convects embedded, frozen-in toroidal magnetic flux from zϭϮh to zϭ0. The counterdirected flows collide and stagnate at zϭ0 and in so doing ͑i͒ convert their translational kinetic energy into heat, ͑ii͒ increase the plasma density at zϷ0, and ͑iii͒ increase the embedded toroidal flux density at zϷ0. The increase in toroidal flux density at zϷ0 increases B and hence increases the magnetic pinch force at zϷ0 and so causes a reduction of a(0). Thus, the flux tube develops an axially uniform cross section, a decreased volume, an increased density, and an increased temperature. This model is proposed as a likely hypothesis for the long-standing mystery of why solar coronal loops are observed to be axially uniform, hot, and bright. It is furthermore argued that a small number of tail particles bouncing between the approaching counterstreaming plasma jets should be Fermi accelerated to extreme energies. Finally, analytic solution of the Grad-Shafranov equation predicts that a flux tube becomes axially uniform when the ingested plasma becomes hot and dense enough to have 2 0 n T/B pol 2 ϭ( 0 Ia(0)/ ) 2 /2; observed coronal loop parameters are in reasonable agreement with this relationship which is analogous to having  pol ϭ1 in a tokamak.