For example in Top Gun Maverick when they have to do the high climb, or in Interstellar in the docking scene what’s happening to their bodies. Also what is the difference between postive and negative g’s?
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When you’re in a car (or plane, or spaceship, or roller coaster) and it speeds up, it feels like something’s pushing you back into your seat. What’s actually happening is the opposite: The car — frame, seats, etc. — speeds up before you do, so the seat pushes on you.
Usually force is measured in Newtons or pounds. But in this case we instead measure it relative to the force we normally feel from Earth gravity. So for example, 3 G’s is an amount of force 3 times as strong as normal gravity.
The human body isn’t a single solid lump. The same logic applies to your internal parts. When you’re accelerating, your bones and flesh speed up first, which means your blood squishes in the direction of acceleration. If it’s only a little bit of force, your heart has no problem pumping your blood back to where it should be. But a normal heart isn’t strong enough to get blood to your brain around 5 G’s; so most people black out somewhere around that amount of force. (And obviously if your brain has no blood for more than a minute or two, you’ll be dead or permanently brain damaged.)
Negative G’s is when the acceleration is in the opposite direction (for example hard braking, or a sudden stop). Instead of experiencing a force pushing you into your seat, instead you experience a force pushing you out.
Again, what’s actually happening is the opposite of what you feel. With negative G’s, you’re thrown forward because the car’s slowing down, but you’re not.
(Negative G’s are why roller coasters have forward restraints and cars have seat belts. To stay safe, you need something that will push you backwards in a controlled way as the vehicle is slowing down. A car stopping immediately — for example running to a wall at high speed in a bad car accident — is an instant spike of very high G force, like tens of G’s. Again, you’re not a solid lump, you have a bunch of different stuff inside you. In this case the force is so strong your organs ram against each other causing invisible internal injuries. Which is why a seatbelt is an elastic restraint, it slowly ramps up the backward force as you continue moving forward, which hopefully reduces or eliminates injuries by bringing you to a slightly-less-sudden stop.)
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