# Why doesn't gravity affect space?

## Amazing facts: why you are really weightless in space

Weight is not kilograms!

It's one of those things about heaviness. If you ask someone: How heavy are you? and he answers, for example: "75 kg", then that may be colloquial, but from a physical point of view this is simply nonsense. Why? Heaviness, i.e. weight, is a weight force and is measured in Newtons (N) and not in kg. Kilograms is a measure of the mass that every body has unchanged regardless of the circumstances, whether on earth or weightless in space. Only the action of gravity on the mass generates a weight F (weight). The two quantities are known to be related to each other via the simple equation F = m * g, whereby in our middle latitudes on earth g = 9.81 m / s ** 2 is the acceleration due to gravity. The correct answer to the question: "How heavy are you? "or" How big is your weight? "should be" 75 kg * 9.81 m / s ** 2 = 735.75 N ". Nobody says anything like that and I would like to bet that very few people realize how wrong it is to give kg.

The force of gravity reaches infinitely far

The kg always stay the same, only the weight changes when you move away from the earth. It decreases quadratically with the distance from the center of the earth, so in principle extends infinitely far into space. Here on the earth's surface, i.e. at 6378 km from the center of the earth, it is 9.81 m / s ** 2 and on the ISS at an altitude of 400 km, i.e. at a distance of 6778 km, it is still 9.81 * (6378/6778) ** 2 = 8.69 m / s ** 2 and thus still 89% like on earth. At the moon it is only 0.03% like on the earth, but that is enough to force the huge mass of the moon on an orbit around the earth.

Also interesting: why most people think wrong

What about weightlessness in space? Let's assume we are on the ISS, so we still have 89% gravity. But because the ISS always flies in a circle around the earth and experiences a centrifugal force that is exactly as great as gravity, both forces cancel each other out to zero. So my weight in orbit has disappeared (a scale in earth orbit shows zero) is because the earth's gravitational force is canceled. My mass remains unchanged.

### Why are you weightless everywhere in space?

Up to this point everything was easy to understand. Now it is getting more difficult: Why are you weightless everywhere in space, even if I fly straight to the moon, like the Apollo astronauts did back then? There is no centrifugal force here to cancel out gravity. The answer is because of inertia. When flying to the moon, the spaceship is braked by gravity. Like braking in a car, this pushes you forward. This is the force of inertia and, like centrifugal force, it balances the force of gravity. In fact, the centrifugal force is also an inertial force, but it acts laterally when I am flying in a circle (accelerating sideways) and the usual inertial force acts back and forth, depending on whether I brake or accelerate in the direction of movement.

What governs the size of my inertia? The answer is, the Lord God made physics in such a way that no matter where you are in space, the inertial force cancels out exactly all acting forces (from the earth, sun, moon, other planets, ...). Therefore one is always weightless in space. The only exception: I accelerate my spaceship with a drive. This pushes me to the floor of the spaceship, which I can measure with a scale. So there is an artificial gravity.

### Why aren't you weightless when diving?

Finally the most difficult question: Are you just as weightless diving as you are in space? The answer is trickier, because a diver doesn't weigh the scales underwater, but he is still not weightless. Why? Weightlessness means "cancellation of all external forces by the inertial force in every point of a body." The underlining is crucial, because both gravity and inertial forces act on every mass point of a body and thus cancel each other out at every point an astronaut in space immediately loses orientation when he closes his eyes, because namely the organ of equilibrium (more precisely his macular organs