Gerrard

true. what I meant was the pressure outside is negative compared to the pressure inside the tote. Therefore, there is a weak vacuum outside the tote as it will draw pressure from the tote. So if the tote internal pressure is below ambient pressure, then there is no movement, but if the tote is above ambient pressure then there is movement? A rocket effect is that there is a pressure imbalance on two sides of the of the tote. The hole side of the tote would have less pressure pushing on it than the opposite side with no hole. So let us say that the internal tote pressure is 20 psi, 5.3 psi would be pushing outward on each side except the side with the hole which would be less than 5.3 psi (rocket effect). Similarly if the internal tote pressure is 12 psi, 2.7 psi would push inward on each side except the side with hole which the inward push would be greater than 2.7 psi (rocket effect because less than 12.7 is pushing on the side with the hole). So shouldn't there be movement even if the pump reduces the tote pressure to 12 psi? You said there wouldn't.

When you pressurize the container, you also create a pressure less than the ambient in the container. If the container was pressurized to lets say 20 psi, the pressure external to the atmosphere would be 14.7 psi and thus negative pressure. (Basically a weak vacuum).

The contents are moving in one direction regardless of whether vacuum is drawing or the container is pressurized. So there should be movement. But Bufofrog (Senior Member) states that there would be no movement if vacuum were drawing. Is that true? Also conservation of momentum definition is "Conservation of momentum is a fundamental law of physics which states that the momentum of a system is constant if there are no external forces acting on the system. It is embodied in Newton's first law (the law of inertia)." So when a pressure differential exists, pressure gradient force exists. Wouldn't this be the force causing change in momentum? If so then force on the container is not necessary in order to conserve momentum? https://www.shodor.org/os411/courses/_master/tools/calculators/pgf/index.html Introduction : This calculator calculates the pressure gradient force (PGF) per mass, in units of km-s-2. Mathematically, we use the sign (+ or -) to signify direction: a positive value indicates from location 1 to location 2; a negative sign indicates from location 2 to location 1. The pressure gradient force moves air from areas of high pressure (H) to areas of low pressure (L). In this calculator, you have three input values: the distance (in km) of the two locations, or centers of high and low pressures the pressure (in kPa) at the first location (the area of low pressure) the pressure (in kPa) at the second location (the area of high pressure) The algorithm for pressure gradient force per mass of air (in the x-direction) is: If the container was pressurized to lets say 20 psi, the pressure external to the atmosphere would be 14.7 psi and thus negative pressure. (Basically a weak vacuum). So if you open the hole on the container the pressure in the container would also decrease, lets say to 16 psi. Based on your explanation, wouldn't the force on walls of the tote be 4 psi in a glass tote and compression in plastic tote? Could it be that the release of extremely high pressure into the atmosphere creates a propeller like effect? See Below. Let's say the tote (pressure rated tote of 2000 psi) was pressurized to 1000 psi. You fully open the valve on the back of the tote and now there is higher than atmospheric pressure immediately behind the tote, perhaps that pressure pushes the tote forward as the pressure moves to low pressure in front of the tote? "Think of a propeller as a spinning wing. Like a wing, it produces lift, but in a forward direction—a force we refer to as thrust. Its rotary motion through the air creates a difference in air pressure between the front and back surfaces of its blades. In order for a propeller blade to spin, it usually needs the help of an engine. " Also if the extreme pressure was being released into a vast vacuum, would it create pressure behind the tote or would the pressure keep dissipating in one direction as there are no molecules to create resistance? Joules-Thomson states that no work is done when the external pressure is 0. But if the external pressure is greater than 0, then work is done. Does this apply to the above scenario?

Yes that is the question. So since you said no, would there be if the tote was pressurized instead of vacuum pulling on it? Since space is a vacuum, how come there would be an opposite force then? When vacuum is "pulling", the container is pressurized in comparison. Either way, the movement is due to pressure differential. Why would there be no opposite force if vacuum is pulling and there would be force when the container is pressurized. Either way the contents is moving toward negative pressure.

You didn't really answer the question I was asking. Is there an opposite force on the tote or cup? Let us assume the drop in pressure in the pump and vacuum is close to -14.7 psig for simplicity.

Let us say you have a tote full of water and you connect an air pump to draw the water using negative pressure generated by the pump and you used a very flexible hose connected to the side of the tote. Would there be an opposite force on the tote moving away from the pump and perhaps even create tension on the flex hose? Let us say you have a cup full of air and you use a vacuum to remove the air from the cup, would there be an opposite force on the bottom of the cup? When wind starts to blow on the back of your head and you feel the wind, why can't you feel the wind push off your face as the air in front of you starts to move away from you?