# Invariant? The hell NO!

1. Apr 8, 2004

### deda

I say the only viewpoint available that provides us with the truth is the center of mass. You go ahead be my guest and choose another but be ware: Your physics will not remain the same. Lets fix the coordinate system on the sun and watch the earth moving. The sun is truly immovable thus has no force on it because of Newton 2. Because of Newton’s gravity sun’s mass is also zero but also and earth’s force will be zero. So how can earth move relatively to the sun? It will probably dilate time and contract space in order to move!

I'm off to Bermuda!

2. Apr 8, 2004

### matt grime

The centre of mass is not a view point. How do you know the sun isn't moving? In another thread you say it is. The sun has zero mass? Bermuda? The triangle, try not to get lost, please.

3. Apr 9, 2004

### deda

If the system is fixed on the sun then the sun in this system is immovable.
If the sun is immovable or has constant velocity due to Newton 1 it is subjected to no force.
If the sun is subjected to no force then due to Newton's gravity the sun has zero mass.
If the sun is subjected to zero force and Newton 3 then the earth is also subjected to zero force.
If the earth is subjected to zero force then its velocity is constant or zero.

In few words we get totally different physics.

4. Apr 9, 2004

### matt grime

The system being fixed on the sun and the sun not moving are, if one assigns meaning to the words that are ambiguous, contradictory statements (the orbits are elliptic).

How do you know the sun is not moving, or moving with no acceleration? In what larger iniertial frame is this observation taking place? Why are you ignoring the other planets in the system?

5. Apr 9, 2004

### Severian596

Many of those few words are "if," and if you can't get past the first statement you have a hard time implying the rest of them

6. Apr 9, 2004

### jdavel

So many errors, so little time!

I'll just straighten you out on this one: "If the sun is subjected to no force then due to Newton's gravity the sun has zero mass."

You need to review the equation for "Newton's gravity" (or maybe 8th grade math). There are two masses in the equation. Only one of them (not necessarily the sun's) needs to be zero for there to be "no force".

7. Apr 9, 2004

### FrankM

How lost am I? That is one of the stangest things I've ever heard. Just because something is not subjected to a "NET" force (notice what I did there with the quotes and capitalizing it?) doesn't mean it has no mass. I am not being subjected to a net force right now (meaning that I am sitting in my chair and not moving, at least my center of gravity is not moving), if I was being subjected to a force I would accelerate. OK so I am not being subjected to a net force (just really bad reasoning) but this in no way means I have no mass. I have mass (a little too much mass actually but such is life in a cube), I can tell by the fact that my fingers actually come in contact with the keys of my keyboard (even though it is mostly e/m fields that are keeping my fingers from going through the keyboard, they would not be there if I had no electrons).

Here is most of the misconception: misinterpreting the math without understanding what is going on. Equating Newton's formula for gravitational force with his laws of motion without a clear understanding of what they mean is ..... meaningless. Sorry but you should probably take a look at a beginning text in Physics.

8. Apr 9, 2004

### deda

Then the earth is the one with the zero mass and you can eat my shorts!

9. Apr 9, 2004

### FrankM

Sorry forgot something
By the way, the sun is not fixed in space, it wobbles because of the pull from the planets.