B Air escaping out of can with hole

AI Thread Summary
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.
versine
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In the first figure, air goes forward and the can goes backward. My question is why does the air exert the pressure gradient force on the can.

Can I have a hint for why the can doesn't move when air is being sucked in in the second photo.
 
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versine said:
Can I have a hint for why the can doesn't move when air is being sucked in in the second photo.
Why do you think it does not move ?
 
I think I got my first question it's because there's more area on the left side of the can.
 
Baluncore said:
Why do you think it does not move ?
Because I saw the answer lol.
 
You do realize that the two scenarios are not the mechanical opposite of one another.
Case 1. High pressure gas in the can exits to lower pressure atmosphere.
Case 2. Atmospheric pressure gas enters into a lower pressure can.
 
versine said:
View attachment 289672
In the first figure, air goes forward and the can goes backward. My question is why does the air exert the pressure gradient force on the can.
Are you asking why the first container will accelerate? Imagine the gas exerts the same pressure on all walls. All wall parts have an opposite wall part, and their opposite forces cancel. Except for the piece of wall opposite to the hole, which has no opposite wall part, and thus the force acting on it is not canceled. So the whole container will accelerate to the left.

versine said:
Can I have a hint for why the can doesn't move when air is being sucked in in the second photo.
The second container will initially accelerate to the right for the same reason. The exterior pressure force on the wall part opposite to the hole is not canceled, because there is no wall opposite to it.
 
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