Stress intensity factor K_I plotted against mean velocities (⁠|${\textit{v}_{\rm mean}}$|⁠) obtained from fluid-filled crack propagating in gelatin. Note that in the assumption of crack propagation with K_I = K_eff(v), the y-axis can also be interpreted as the gelatin's effective fracture toughness. (a) Cracks filled with viscous fluid (silicon oil) and volumes ranging from 10 to 50 mL: 10 mL in squares, 30 mL in triangles, 50 mL in diamonds and others in circles (Table 1). (b) Cracks filled with non-viscous fluid (air) and volumes ranging from 1 to 10 mL (Table 2). For each set of experiments, the dashed lines represent the linear regression of K_I as a function of v_mean: K_I^(oil) = 404.9v + 2.2 and K_I^(air) = 1.2v + 24.0.