Brian Cox

Chippy_boy said:
On the subject of gravity, here's another proof:

Does hodge have Sky, I wonder? If so, his satellite dish is pointing at a satellite (Astra, is it, or Hotbird? I forget). These satellites are in geostationary orbit, so they remain in the same position the sky. If gravity exists (which it must, or we'd all be floating around the room), why don't these satellite fall to earth? What's keeping them up?

What's keeping them up is them orbiting our rotating planet at a speed of about 3km per second. So that the centrifugal force perfectly counteracts gravity and they don't fall to earth and don't fly off into space either.

This would be impossible if the earth was flat. Sky satellites would just fall to earth. There would be no Sky TV.

I suspect this piece of evidence may be a bit beyond Hodge's comprehension however!
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In fairness a little beyond most folks comprehension and it's Astra. A serious question posed Chippy. Is the given speed critical to keeping these satellites in fixed orbit and if so how was the correct speed calculated for them not to fall to earth or drift away into deep space.

And one last question as this could prima-facially be called a techie thread..We were sat on the balcony last night having a session and enjoying the downpour and the coolness in the air was overtly noticeable.My question concerned our suns energy and heat output.How can it be hot at street level and yet when you go up in a plane and are closer to the sun the temperature drops below zero.Maybe a question for one of our resident pilots or physicists.
 
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Two Gun Bob said:
In fairness a little beyond most folks comprehension and it's Astra. A serious question posed Chippy. Is the given speed critical to keeping these satellites in fixed orbit and if so how was the correct speed calculated for them not to fall to earth or drift away into deep space.

And one last question as this could be prima-facially be called a techie thread..We were sat on the balcony last night having a session and enjoying the downpour and the coolness in the air was overtly noticeable.My question concerned our suns energy and heat output.How can it be hot at street level and yet when you go up in a plane and are closer to the sun the temperature drops below zero.Maybe a question for one of our resident pilots or physicists.
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The actual difference in proximity to the sun is negligible. The sun is approx 100,000,000 million miles from Earth. The top of Everest is something like 30,000 feet.

The colder temperatures at altitude are all down to atmospheric pressure. The higher you go, the less pressure on the air. Lower pressure = lower temperature.
 
Two Gun Bob said:
In fairness a little beyond most folks comprehension and it's Astra. A serious question posed Chippy. Is the given speed critical to keeping these satellites in fixed orbit and if so how was the correct speed calculated for them not to fall to earth or drift away into deep space.

And one last question as this could be prima-facially be called a techie thread..We were sat on the balcony last night having a session and enjoying the downpour and the coolness in the air was overtly noticeable.My question concerned our suns energy and heat output.How can it be hot at street level and yet when you go up in a plane and are closer to the sun the temperature drops below zero.Maybe a question for one of our resident pilots or physicists.
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Its very simple. The sun heats the ground, not the air. And heat radiates out into space.

So the closer to the ground you are = more heat up and less lost to space = higher temperature

So higher up you go, you are further away from the heating effect of the ground and there's also more heat loss into space. Therefore lower temperature.
 
Cheesy said:
The actual difference in proximity to the sun is negligible. The sun is approx 100,000,000 million miles from Earth. The top of Everest is something like 30,000 feet.

The colder temperatures at altitude are all down to atmospheric pressure. The higher you go, the less pressure on the air. Lower pressure = lower temperature.
Click to expand...
Drops about 1 degree per 1000 feet IIRC.
 
Cheesy said:
The actual difference in proximity to the sun is negligible. The sun is approx 100,000,000 million miles from Earth. The top of Everest is something like 30,000 feet.

The colder temperatures at altitude are all down to atmospheric pressure. The higher you go, the less pressure on the air. Lower pressure = lower temperature.
Click to expand...
Pressure and temperature are not dependent on one another. Temperature of a gas is a function of the speed of the molecules, not how many of them there are.

Pressure is not the reason it's colder higher up.
 
Two Gun Bob said:
In fairness a little beyond most folks comprehension and it's Astra. A serious question posed Chippy. Is the given speed critical to keeping these satellites in fixed orbit and if so how was the correct speed calculated for them not to fall to earth or drift away into deep space.

And one last question as this could prima-facially be called a techie thread..We were sat on the balcony last night having a session and enjoying the downpour and the coolness in the air was overtly noticeable.My question concerned our suns energy and heat output.How can it be hot at street level and yet when you go up in a plane and are closer to the sun the temperature drops below zero.Maybe a question for one of our resident pilots or physicists.
Click to expand...

Sorry, missed your first question.

It's simple maths (in principle). The centifugal (or centripetal) force must match the gravitational pull. Fa = Fg.

Gravitational pull Fg = (G x m1 x m2)/r^^2 (G is the gravitational constant and m1 is the mass of the earth, m2 is the mass of the satellite) r = is the distance from the centre of the earth to the satellite

And the centrifugal force Fa is given by m2 x v^^2/r. Where m is the mass of the satellite, v is how fast it's going and again r is the distance from the centre of the earth.

Solve the equation (m2 cancels out) and you have the relationship between height and speed, in order to balance the two forces. However, we know how fast the earth spins, so there's only 1 speed and height which keeps the sateliite stationary in the sky. It's about 22 miles up and about 7,000 mph.
 
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