Question on Gravity?

They have known this for around 400 years.

And there is gravity in space. In orbit, its not much different to here on earth. Weightlessness does not occur because there is no gravity but because there is no net force.

This was also know around 400 years ago.

Sounds like you're confused (like most people, I'm afraid). There *is* gravity in space. Gravity is everywhere - the force of gravity extends infinitely far. Of course, it also gets smaller as you get farther away from an object.

The space shuttle, as an example, orbits Earth about 200-300 miles above the surface. Since Earth is 8000 miles across, the space shuttle is still very close to Earth - what we call low Earth orbit. The force of gravity on the shuttle is about 90% what it is here on the surface of Earth. The reason everything floats in the space shuttle is because it and everything in it are in free-fall.

We've always known that things in orbit would be apparently weightless, at least ever since Newton figured out the mathematical formula for the gravitational force between two objects.

Here's a website that explains it:

http://www.nasa.gov/centers/glenn/research/microge...

That's a good question. Both the Greeks and Phoenicians knew the Earth was round more than 2000 years ago, so it must have occurred to them that on the other side of the world , gravity pulls you in the opposite direction. Two thousand years later, Newton worked out that two masses, like you and the Earth, attract each other with a force that's proportional to the two masses multiplied together and inversely proportional to the square of the distance between their centres. He realised that if you're far enough away from Earth, its gravity is negligible, and that when you're in orbit, you're falling continuously, so you feel weightless, just like in a lift when the cable breaks. Yuri Gagarin, the first man in space, was trained for microgravity in a lift at Moscow University, which is a high rise building. The cable was disconnected and it was allowed to free-fall. At the bottom, air brakes brought it to rest safely.

Yes, everyone knew the astronauts would be weightless in space. It was in all the books long before the first person went to space. I believe Jules Verne's book, from the Earth to the Moon, written in 1865, mentions it.

From the very first one, all space craft have been designed with weightlessness taken into consideration.

However, the others who say there is gravity in space are correct. It is the motion of the space craft as it coasts in orbit that causes the weightlessness, not a real lack of gravity. Every time you jump up, you are weightless until you land again, only in space it goes on and on, not just for a second.

It's not that there is no gravity, it's that as one moves farther from a planet the effect of gravity due to that planet lessens, following the equation for finding the force due to gravity:

(GM1M2)/(R+d)^2

The universal gravitational constant muliplied by the mass of the planet, times the mass of an object (the satelite or spaceship) all divided by the radius of the planet plus the distance from the surface of the planet, product squared.

By following this equation early astrophysicists knew that there would be negligible gravity once you achieve a certain distance from the earth. It's all basic physics, so of course such things were taken into account.

There is gravity in space. What is going on is that the ship and everything in it is free-falling to the earth but as it falls it also keeps moving forward and therefore falls into the orbit around the planet. Everything is moving and falling at the same velocity and it gives the effect of "zero gravity" which indeed is an unfortunate misnomer.

Let us consider the solar system alone.

All planets and objects like satellites are attracted by the gravitational pull of the sun. This also implies that sun is attracted by those objects.

Hence you cannot imagine a space within the solar system where there is no gravitational field.

But the question of the path of these objects within the solar system depends upon the energy possessed by these objects and the proximity with other objects.

That's a good question. I'm sure they knew there was no gravity before they sent up the first astronauts as there were already satellites in space at the time.

They knew for 100's of years that there was no gravity in space. They used to call space "ether" for 100's of years.

Of course, there is gravity in space or we'd all go flying off; nthing be able to remain in orbit, either. You are referring to weightlessness which is something different.