How is it that no one ever noticed that there was gravity before Sir Isaac Newton appeared?

I think it’s safe to assume that people have always noticed when, for example, they fell from a tree or mountain and hit the ground.

Newton’s great scientific achievement was to realize that it is one and the same force that holds the Earth on its orbit, the moon on its orbit, and drops the apple to the ground.

If an Earth-trabant – be it the moon, or an artificial satellite, of which of course in Newton’s time was not mentioned – is subject to the gravity of the Earth, how is it that the moon does not fall on the earth like the apple?

Newton provided the explanation immediately.When a stone is thrown parallel to the earth’s surface, it falls back to Earth in a parabolic arc. The faster the stone is thrown, the flatter the arch. At some point, the arch is so flat that it coincides with the curvature of the earth. The stone falls and falls – but around the earth, and not on the ground. That’s why satellites stay in the sky for a long time, and nothing else does a rocket do when it brings a satellite to a height and speed that the satellite falls around the Earth.

One often learns that a satellite stays in the sky because centrifugal force and gravity would pick up exactly.Centrifugal force depends on the reference system – in the satellite’s coordinate system there is only free fall around the earth.

The fact that one is weightless in free fall is investigated in Einstein’s General Theory of Relativity.

That is why there are also these fall towers, where the influence of microgravity can be investigated for a few seconds.

Astronauts on the ISS or in a space capsule are weightless because they are in free fall around the Earth.

Why not be weightless on the moon when it falls around the earth?

Well, for the same reason that one is not weightless on earth, even though the earth falls in free fall around the sun: the masses of the moon or the earth.Earth is so big that they can build up so much gravity to attract objects.

Because the Earth is much more massive than the moon, its gravity is so great that it can hold a gas atmosphere in which we can breathe.The moon’s gravity is so low that each gas simply escapes from the moon’s gravity field. That’s why the Apollo astronauts needed spacesuits with oxygen tornisters on their backs. But it is still enough that people there could hop and perform quite artistic tricks.

Pack a backpack of 30kg on your back and jump out of the push-up on your feet…

There is still a lot to write about gravity.No one knows where it comes from and why crowds attract other masses and why crowds are sluggish. One can only describe how gravity affects masses.

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