Air exerts a pressure gradient force on the can due to the difference in pressure between the inside and outside, causing the can to move in the first scenario. When air is sucked into the can, it does not move because the external atmospheric pressure acting on the can's walls is balanced, preventing acceleration. The forces on the can are not canceled out in the first case because the wall opposite the hole experiences an unopposed force. In contrast, in the second scenario, the can initially accelerates to the right due to the same principle, where the external pressure is not countered. Understanding these dynamics clarifies the behavior of the can in both situations.
