You don't see that Dave is being deceitful trying to set up a trap for his opponent? It's a common enough practice even among Christians debating the differences between their denominations. This may not be the best example, but I think you'll understand what I'm getting at. Someone may nail down the teaching of Romans Ch 13 that we must obey authority, and resisting it means we resist God and will go to hell. Then they say how can you resist such and such authority (Pope, diocesan clergy, civil authorities, ect) at all? Then you'll be like "but, but, but". No you said Scripture has such and such authority, and the Church teaches obedience just like Romans 13.
Dave is actually biasing himself against what may be the truth before asking the particular question, whether just to get views and praise from his audience or because his is of bad will, who knows. It's like he's trying to harden his heart before being confronted with the truth.
There are a variety of forces, some large, some very small. In any circuмstance we will normally encounter, the forces involved with gas pressure equalization is going to dominate since it is far greater than the effect of gravity.
1 liter (think a quart jar) of water weighs 6lbs, 1 liter of air weight 1.3 grams (the weight of a small paperclip). 1 liter of air in the size of a quart jar (excluding the weight of an actual quart jar) sitting in your hand will exert about 0.003 pounds per square inch of pressure on your hand. The air pressure around you is almost 14.7psi compared to a vacuum which is 0psi. What is 0.003psi compared to 14.7psi?
14.7psi at sea level, but why? Why does air pressure decrease with altitude? The air has mass. Anything with mass is affected by gravity. If you don't want to believe in gravity, call it what you like, but things with mass do fall towards the ground if no stronger force is pushing them away. Air does have mass, demonstrated by the fact that its movement affects other objects with mass, and that cold air (denser) can be observed to fall while warm air (less dense) rises. We know that when you stack things, the whole lot gets heavier. Stack ten 20lb weights, and the whole stack exerts 200lbs on whatever it is stacked on. The weight on top only presses down with 20lbs on the other nine weights below it. It's the same with air. The air above weighs down on the air below with the weight of the air increasing as the stack of air is taller.
How to imagine air sticking to a globe earth in the vacuum of space:
Imagine a big empty vacuum chamber. Then imagine a jar of air is opened in this vacuum chamber, and imagine this air is dyed yellow and somehow made to be attracted to a magnet like steel. So now it looks like a cloud of yellow smoke rushed out of the jar and evenly distributes itself in the vacuum chamber. What happens if you put a strong magnet in the middle of the vacuum chamber? The yellow magnetic air molecules would rush toward the magnet making a cloud of yellow around it.
If you have ever played with magnets, they will pick up many small nails or paperclips, but the nails furthest from the magnet are attracted weakly, while those touching the magnet are very strongly held there. The cloud of yellow air around the magnet would do something similar, collecting more densely immediately around, while less densely further away.
What makes air rush into a vacuum? Vacuums (low pressure) don't actually suck, rather things are always blown into a vacuum or a lower pressure zone by pressure. Air particles jiggle around and bump into each other pushing each other away. This is temperature. Absolute zero temperature would in theory mean that no atoms jiggle around at all, therefore no pressure caused by the gas trying to push itself to spread out.
Gas pressure is caused by gas particles colliding. If gas particles do not collide, like when they are spread out in a vacuum, then nothing is pushing them around, so gravity can attract them in a general direction. As gas particles congregate around a source of gravity, they will get so close to each other as to start colliding. Any particles that get bounced away from the gravity source by the other particles will either crash into many more air particles attracted by gravity, or none at all and eventually start falling back toward the source of gravity. With the majority of the particles trying to move toward the source of gravity, the sum of the forces will be in that direction, causing the particles closer to the source of gravity to be under the weight of those above. This makes for a very dense layer near the ground, and a very spread out low density layer above.
This is what we observe, because people have trouble breathing above 2-3 miles altitude, while airplanes can fly up to around 15 miles high, balloons up to 25 miles, and there's still air (though very little) extending more than triple that. Most of the air, the air of high pressure, is contained in a small fraction of the total altitude that the atmosphere extends above the surface. This demonstrates how weak gravity is compared to the force of air particles colliding with each other, and that with enough low density air held in by gravity, the air below it gets all the more concentrated and doesn't just rush out into a vacuum.