# ELi5 : Please explain G-forxe in simple terms

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ELi5 : Please explain G-forxe in simple terms

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A forced is defined by:
F( Force)=m(mass)*a(acceleration)

Gravity , for exemple on earth, exert a specific amount of acceleration towards the (here) planet to an object.
This acceleration ist called g

G-force (gravitational force) I therefor the force that is exerted by gravity.

It is used as a scaling to compare Different impacts on a Objekt

“G-force” is the feeling of your speed increasing or changing. When you “put your foot down” i.e. accelerate in a car you feel a g-force due to the car moving faster and your own body reacting by being “pushed” back into your seat.

It’s called “g” force because you have the same sensation all the time being pulled to the ground by *g*ravity. The two sensations are technically indistinguishable if you get into the physics of it.

In simple terms.
G stands for gravity. So… let’s say you are travelling in a vehicle and reach 3Gs. That’s means you are moving at a speed that is equivalent 3 times the force of gravity in your body.

One G is the effect of Earth’s gravity. It’s what you feel every day, walking around, trying to get up from a chair, falling after tripping over.

If you’ve ever been in a lift/elevator, you will know what it feels like to experience more or less than 1G. Do you know that feeling as the elevator car starts to go up? It feels like you’re suddenly heavier until the car gets to a constant speed. That is the experience of more than 1G.

Similarly, do you know that feeling when you’re using a lift to go down, when the car starts moving, and your stomach flips? You’re experiencing less than 1G.

It’s important to understand that these changes in G-forces in an elevator, are *exactly* the same as being in a lower/higher gravity environment.

Even so, a lift/elevator is specifically designed to not accelerate you too much, meaning you won’t experience G-forces that are much different to 1G.

But under some circumstances (e.g., where a fighter pilot is changing direction (i.e., accelerating) quickly), they will experience a big change in G-forces. This can lead to blacking out or redding out when they experience very high or very low G-forces, respectively.

Accelerating in any direction causes you to feel a force, following the equation f = ma, where m is your mass.

You feel this force when you’re in a car accelerating, or in a train, or a rocket going up to space, wherever.

“G-force” is just measuring that force as a multiple of the force due to gravity. 1g is the force you feel pulling you to the ground. 2 g’s is twice as strong as that. 3 g’s is three times as strong. And so on.

It doesn’t mean the force you’re measuring is caused by gravity. When we say astronauts are experiencing 3 g’s during a rocket launch, that force is due to the rocket, not due to gravity. We’re just comparing its strength to the force from gravity.

Once of the things we are all familiar with is what it feels like to sit or stand or to walk around. When we sit on a chair and the chair pushes up on our bottom to stop us from falling downward it feels one way. When we are standing or walking on a flat surface the floor pushes on our feet in a way that we feel particular sensations. At the same time, every part of our body is being pulled downward by gravity – when you hold out your arms, your muscles in your shoulders need to stay tight to prevent the arms from falling down, and all over the body different muscles are working to keep your body parts where you want them rather than letting those parts move downward the way gravity is pulling them, and your nerves can feel information about all of these things. This is what “1 G” feels like – the downward force of gravity acting on your muscles combined with the feeling of the upward push you feel from whatever you are sitting or standing on.

If the box starts to move upwards (like an elevator) the bottom of the box pushes against your feet with more force, and your muscles need to push harder to keep your body parts where they are in relation to the bottom of the box, which is now moving upwards. If feels like you have become heavier – if the box accelerates upwards at about 1 meter per second each second, you will feel about 10% heavier which might be described as “1.1 G” or “1.1 G-force upwards”.

If the box starts to move downwards (like an elevator) the bottom of the box pushes against your feet with less force than normal, and your muscles need to push less to keep your body parts where they are in relation to the bottom of the box, which is now moving downwards. If feels like you have become lighter – if the box accelerates downward at about 1 meter per second each second, you will feel about 10% lighter which might be described as “0.9 G”.

Surprisingly (it is surprising to me at least), nobody has ever figured out a test to distinguish between being in a box that is just stationary on the earth’s surface, and being in a box in outer space that is accelerating upwards at “1 G” (a little bit less than 10 meters per second each second). The “force of gravity” seems to be identical to “accelerating upward at 1 G”.

All of these feelings are different when the floor or the chair is tilted. If you are inside a big box, and the box gets tilted, you can feel that you are pulled downward towards the low side of the box. This is still “1 G”, but now it is at an angle rather than being straight towards the “bottom” of the box. If you drop a ball in a tilted box, it falls “straight down” but that direction is no longer perpendicular to the “floor” of the box, since everything is tilted. As you stand there, the floor still pushes straight against the bottom of your shoes, but now also the soles of the bottom of your shoes prevents you from slipping.

This is almost exactly the same feeling as if the box was not tilted but instead was being accelerated to the side at 1 meter per second each second. The bottom of your shoes grip the bottom of the box as it moves to the side, and it feels like one side of the box is higher than the other side of the box – you need to lean “uphill” in the direction that the acceleration is. This is what you feel in a car when it accelerates form a stop, but it is more easy to view in a long object like an airplane speeding up along the runway or a train pulling out from the station. The front of the train seem to be “uphill” and a ball will seem to fall at a tilt if you trip it. The “g-force” seems to push you back into your seat even though someone looking at you from outside the box would realize that the seat is pushing you forward as the box/car/plane/train speeds up.

When the box/car/plane/train moves at a constant speed, everything feels the same as if it was not moving at all – down feel like down, and things drop in the normal manner.

If the vehicle slows down, everything gets weird again. The seatbelt needs to pull you backwards to slow you down along with the vehicle (or the grips of your shoes pull you backwards if you are standing), and now it feels exactly like the box/car/plane/train is tilted downwards. It feels like there is some force pulling you forwards.

Similarly, if the vehicle turns to the left, the seat or floor will pull you to the left and your body will need to react in the same way as if gravity was pulling it “down” to the right. Thus on a bike you “lean into” corners, and on a roller coaster you squish your little brother as you slide outward along the seat in a tight corner.

Fighter jet pilots can feel extreme “G-forces” as their plane makes tight turns left, or right, or up, or down. Their bodies can be pushed around so extremely that not all their blood is unable to stay up in their brain where it is needed, and they might pass out. It *feels* like the blood is pulled down out of their head when they curve their plane upward, but really it is their head that is being accelerated upwards and the blood us being left behind.

All that is probably more detail than a five year old really wants I suppose…