Scientific question(s)

[Sqrl]

mrstickball said:

Kantor said:
I have a question.

The Sun is larger than the Earth, and thus has a stronger gravitational pull. It is strong enough to keep something as massive as the Earth in orbit. So why isn't it strong enough to pull all of us in?
Is it something to do with distance? So if gravity on Earth stopped, we'd all be pulled into the Sun?

There are a few answers to that..

1) It's not strong enough to pull us in because the Earth has gravity too - enough to keep us here, as gravity exerts a downward force to keep us on the ground.

2) The further you get away from the sun, the less effect the sun has on gravity. In order to stay in orbit, the object requires an orbial velocity. The closer an object is to the sun, the faster it must move to prevent getting sucked in. For example, Mercury's speed is 47.9 km/s, whereas Earth is 29.8 km/s.

3) The idea of gravity stopping on earth, and the effect goes against the laws of gravity. To have no gravity on earth requires no earth. The assumption would be that if an object was moving at no speed (which no object is), then it should get pulled into the sun, provided it didn't get too close to another planet and become captured by it.

 

 1) You and Fayceless have the right idea but gravity isn't actually exerting a force (otherwise you could express gravity in newtons), it is more of a missunderstanding between what a straight line actually is within space-time.  We tend to view our world from a Euclidian Geometry viewpoint, which in most mundane matters on Earth is perfectly indistinguishable from non-Euclidian Geometry, but in reality the gravity isn't exerting a force so much as changing the definition of a straight line within the gravitational field by curving space (ie its more apt to call it a geodesic than a "straight" line).  In effect the definition of a straight line is bent/curved by gravity and the object travels the "straight line" as it has been redefined within the warped space.

This picture may be odd but these are all examples of straight lines in their respective types of geometry. Note that in each case the two "parallel" lines have a perpendicular line between them which meets them at a right angle as it is defined within the respective geometries (also note this is a 2d representation of something that actually occurs in 3d, so its not exact):

 

As I said it can be a bit odd to wrap your head around it. 

2) The best way to describe this is that the Earth wants to fly off into space and the sun is "bending" the definition of a straight line such that the "straight line" of flying off into space actually curves by the sun.

3) Don't really have anything to add to what you said here.

PS - I know this was probably a bit of nit-picking, so please don't take it the wrong way. Just something I don't think very many people know about.