Gravity in a hollow Sphere

So This blog has taken a bit of an environmental slant, but that is because that is what was on my mind - but it is not all I think about.

Recently I was talking to a colleague about physics, and we got onto the subject of gravity in a hollow sphere - don't ask how we got there, I have no idea.

Any way My colleague said that in a Physics class he had learned that there was no gravity in side a hallow sphere. Ever since I was pretty young I have pondered the idea of what happens to gravity at the centre of the earth, or any other spherical object, I had sort of assumed that there would a a point where Gravity would be Zero - because there is an equal ammount of earth each side of you, so the gravitational force exerted by one side would the equal to the force from the other side, so you wouldn't move if you were right in the centre (ignoring all the other problems you would be having) I had assumed that as soon as you move from your place in the centre, you would be closer to one side than the other and the gravity from the closer side would have a stronger pull than that from the further side and you'd end up stuck to the wall.

However according to the Gauss-Ostrogradsky theorem at every point inside a hollow sphere gravity is Zero. there is all sorts on nasty math to "prove" this but I think the general idea is that if you move off your point at the centre, there is more sphere behind you than in front, so the fact that is further away is made up for by there being more of it, so the force exerted by the wall in front and behind you are still the same. I am still not 100% convinced - I think a practical demonstration is called for.

The end of Incandescent bulbs in Canada

Yep, Ottawa has decided to phase out the old incandescent bulbs by 2012 for the full story visit CBC.
I think this is more of a political move, but it is a sign that the government has realized that the public are becoming more aware that we are of what we are doing to our environment.
The fact that there is enough concern in the public that it has a political significance is encouraging. Hopefully this is the first step on a new path that will see our government take a lead in implementing environmentally conscious legislation.