A dislocation in a crystal lattice, a disconnected region in its structure (represented by the array of atoms shown in blue) can separate from the rest of the lattice at a rate determined by the potential energy of the system, represented by the wavy surface. To the left, the higher potential energy (shown in red) prevents the defect from moving in that direction, but to the lower right (shown in blue) the defect can glide toward a lower-energy state, if it first overcomes the higher-energy hump. Once over that hump, it can move rapidly and continuously — a condition called flow stress.