16 Jun '08 10:42>
Isn't the Earth heavier in the US?
Originally posted by twhiteheadDon't forget that our Solar system also has some acceleration according to another reference point. Is it even possible to find a sort of unmoving point of the Universe according to which we could calculate weight? Are there any completely unmoving objects? Is that even determinable?
Thats nonsense. They do not lie on a straight line.
I think that the easiest way to find out the gravitational force acting on a body is to know the bodies acceleration and mass and work it out from there. The earths acceleration is almost entirely due to the sun, so I think we can quite easily ignore all the planets - and the rest of the universe too.
Originally posted by kbaumenThere are no fixed points in the Universe. Unless you define one.
Don't forget that our Solar system also has some acceleration according to another reference point. Is it even possible to find a sort of unmoving point of the Universe according to which we could calculate weight? Are there any completely unmoving objects? Is that even determinable?
Eh, sorry if that sounds like nonsense, just some questions (rather philosophical though) that popped to my mind while reading this discussion.
Originally posted by kbaumenYou can assume any point in the universe to be immobile for the purposes of calculating acceleration. Of course, that doesn't mean that the point in question really isn't moving, it's just defined not be moving relative to its initial position.
Don't forget that our Solar system also has some acceleration according to another reference point. Is it even possible to find a sort of unmoving point of the Universe according to which we could calculate weight? Are there any completely unmoving objects? Is that even determinable?
Eh, sorry if that sounds like nonsense, just some questions (rather philosophical though) that popped to my mind while reading this discussion.
Originally posted by PBE6But the earth is constantly accelerating directly towards the sun. (Velocity is not the key here but acceleration).
For the purposes of calculating "weight" (i.e. the vector sum of all the gravitational forces acting on a body), the acceleration isn't needed since there's no guarantee the body in question is moving in the direction of the weight vector - even though the weight vector for the Earth points pretty much directly towards the Sun, the Earth moves perpendicular to that direction in its orbit (for the most part).
Originally posted by twhiteheadActually, that's right, the Earth is accelerating towards the Sun. However, not all bodies with weight accelerate in the direction of their weight vector. A rocket is a prime example - something designed to provide enough force in the opposite direction of its weight vector to overcome it and accelerate away. That's why I think all this talk about relative motion is beside the point.
But the earth is constantly accelerating directly towards the sun. (Velocity is not the key here but acceleration).
The earths acceleration is almost entirely due to the sun, so any other accelration can be essentially ignored. (we do the same when calculating the weight of objects on the earths surface (they always accelerate towards the earths centre a ...[text shortened]... when it comes to the earths orbit, we would have to factor the moons mass into our calculation.
Originally posted by PBE6They do when they are in free fall ie do not have a force acting on them other than gravity. This fact enables us to use an objects acceleration to work out its weight. In fact that is the usual method of determining mass.
However, not all bodies with weight accelerate in the direction of their weight vector.