What if I jump sideways. Wouldn't the pressure want to push me back instead of letting me carry forward with my momentum when I lost my balance because I'm old and fat. Why does it only work downward?
Imagine being under a super slippy rubber sheet covering an area.
You're laid down and it covers you.
Think of this as the atmosphere laying on you.
Ok now you get up and realise that you have to push this slippy thing away from you but as you do, you stretch it which places a lot of extra weight on your head and shoulders and now your legs because you are trying to force this out of your way.
You are now stood up and this rubber sheep takes your form.
So basically you are covered all over by the sheet.
It's so slippy that you can take a step forward in it and it will simply slide behind you but the sheet in front will cover you as you do this.
No matter what you will always be covered.
If you try to jump up into it, you realise that it can't just slip off you, because you are vertically pushing into it and compressing it it and yet that compression springs right back onto you and around you as it covers you.
The only thing stopping it pushing you into the ground is your feet and the density of the ground.
Ok so let's say you want to run. As you run you push into the rubber but as you do more rubber just cascades down onto you. A resistance to your run is always there and you cannot escape it....but, there is help in the fact that for every action there is an equal and opposite reaction.
You see, as you run into the rubber you compress it or push it out of the way, This is channelled around you and fills the area you ran away from, because you are running away from the rubber so it can'y quite envelope you at the back until you send the compressed rubber around you to hit the slow filling void.
This then crashed into the rubber behind and right back onto your back with the same force that you push at the front with.
As this happens, the rubber is always trying to compress down onto you and that is why when you run you run with your body angled forward, including your head when you need to accelerate, because to accelerate means you have to add more compressive force to gain the required reaction behind.
This is why it's difficult to stop when you run and especially accelerate.
a human like analogy would be to imagine you are in a race in a single file.
As you race you have to run into people coming at you in double file. This is your compression force from your front push.
I am behind you in double file leaving a small gap.
You push into the middle of the people and force them around you.
They crash into the double me and I crash into them, pushing them back onto you as you hit the next two coming at you. And so on and so on.
Equal and opposite reaction to your action.