A vending machine that forms a perfect rectangular prism and stands upright with dimensions of height 2.0 meters, width 1.2 meters, and depth 0.6 meters. This machine is loaded onto a van with the side measuring 1.2 meters aligned with the vehicle's forward motion. Given that friction between the machine and the van's floor prevents sliding, determine the highest possible acceleration of the van that would not cause the vending machine to fall over. Hint: Analyze the situation by considering the action of the normal force at the critical edge along the base of the machine.