Behavior of Gases: How we experience the every day consequences of gas particle behavior 

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It's been passed down from my great great great grandmother from Vladivostok. Glad to find new uses for it.

I just lift the edge of the lid, which allows air to come through and fill up any space below the lid, which restores the pressure balance, and so gravity is the only force that is felt.

The upward force from the table is called the "normal force" which only accounts for the table being able to stop the lid from going further toward the floor due to the repulsions between electron clouds in the atoms at the table surface and in the atoms on the bottom surface of the lid. The normal force here is quite tiny. The real equilibrium is between the bonds holding the table's atoms together and the electron repulsions between the two surfaces and the two downward forces of gravity and air particle collisions on the outside surface. There also will be an equilibrium within the cup itself once air is restored at the bottom surface and the lid can go back to its lowest PE shape.

@@CrashChemistryAcademy No. I beg to differ. Let's do this in steps. Step 1: Let's consider the situation where you have just pressed down the cup and removed your hand. So the object is sitting on the table flat. Let's do a free body diagram for the object on the table. The downward force of its weight plus the force from air particles above equal the surface normal force from the table. Do you agree? This normal force is NOT tiny and in fact is doing most of the heavy lifting. Step 2: You apply a force upward using your hand. The weight plus the pressure force from above have not chanced from step 1. These forces plus the force from the table will resist the lift force from your hand. The role of the normal force is critical. You can imagine another situation where you press the cup hard on a vertical wall and it sticks (like a plunger). The surface normal force will equal to that of the air pressure.

@Nikan Rst I mostly agree with your clarification. Problems: 1) Lifting the object does the opposite of resisting. It's elasticity "pushes" it upward from the center, which is how a suction cup works, so lifting it is helping it get where it "wants" to go. The resistance you feel is the outside air pressure pushing it down, plus a little gravity (as you say). But what specifically is the attractive force between the cup and the table are you are referring to? 2) I do not agree with your original assertion: "when you pull on the cup to lift it you are trying to overcome the force exerted between the cup and the table." This cannot be the case since there are only repulsive forces between the electrically neutral lid and the electrically neutral table, that of electron repulsions between the two surfaces. While we can speak of momentary dipoles created by those repulsions, they are negligible due mostly to the large distance (microsopically speaking) between the surface atoms of the two surfaces and the microscopic irregularity of their surfaces, which incidentally allows a small amount of air to stay between the two surfaces, although not enough to have any apparent opposing force to the outside pressure. The change in the normal force is only due to the gravity exerted on the object. The normal force countering the air pressure on the suction cup is the same on the entire table: atmospheric pressure is always present on the table regardless of any other mass placed on it. Also, my referring to the normal force as tiny was coming from my own (unstated) comparison of the very strong atomic interactions in the table, and the large repulsions between electrons at the two surfaces, versus the relatively much smaller calculated normal force, whatever that would be.

@@CrashChemistryAcademy ​ @Crash Chemistry Academy Let me write the force balance equations: Step 1: object pressed to the table- hands off : Weight (cup/lid) + air pressure force = normal surface force from table = this is a constant value Step 2: trying to lift the object using your hand (let's just call it lift) weight + air pressure force = lift + a new force acting on the cup from table we may wonder, why should there be a new force acting on the cup now? remember the left hand side is a CONSTANT value so it cannot change, but the force from your hand can vary, as demonstrated in your video ,,,the harder you pull, the more resistance you feel This means a new force is now resisting your pull to balance the equation above The lift force is the combination of the air pressure, the weight AND this variable force whose value depends on how much force you use to pull the cup with That's my understanding of the situation.

Nikan Rst Well in my opinion the Jedi are evil!

Thanks!