Can the momentum of the sun be affected by the energy it produces?

In summary, the sun has a certain amount of momentum, but it is slowly decreasing due to the energy it is constantly producing. Conservation of momentum mandates that this change should be very small, but it is actually measurable.
  • #1
Erizo
1
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I was wondering: From the point of view of an observer who is in motion relative to the sun, the sun has a certain measurable amount of momentum. However, since the sun is constantly turning mass into energy via a nuclear reaction, yet its velocity remains more or less stable, that momentum should be very slowly decreasing. That would violate conservation of momentum.

The only way I can see around this is if the energy being produced has momentum of its own. So can energy have momentum? Does anyone know if it's possible to measure the momentum of, say, a beam of light?
 
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  • #2
Light has momentum, definitely.

[tex]p_{photon} = \frac{h}{\lambda }
[/tex]
 
  • #3
Erizo said:
However, since the sun is constantly turning mass into energy via a nuclear reaction, yet its velocity remains more or less stable, that momentum should be very slowly decreasing. That would violate conservation of momentum.
Why would that violate conservation of momentum? If the mass is changing, the momentum must also.
 
  • #4
Erizo;

First off momentum IS conserved. Keep in mind that all the mass thrown off as radiant energy and solar wind is going someplace. It didn't just disappear. And from a conservation of momentum point of view you have to count that. When you do you'll see that momentum is in fact conserved.

Secondly the Sun's movement through the cosmos isn't determined ONLY by its momentum. It's not an isolated system. It's being pulled on by everything else in the universe. The more massive and closer things are the more effect they have, but even the tiniest sub-atomic particle on literally the other side of the universe has at least some effect on the Sun's movements, its "speed".

Just for example, consider this - if momentum was the only force acting on the Sun then it'd be traveling in a nice straight line instead of orbiting the center of mass of our Galaxy. That right there should tell you that gravitation pull from other objects in the universe have more effect on the Sun's path then its momentum.

Lastly, from a simple accounting viewpoint, if you don't want to count the mass of the Sun lost to radiant energy and the solar wind as being part of "The Sun" proper, the star being observed, then yeah, the momentum of what you're calling "The Sun" IS dropping exactly in line with the amount of mass it's loosing.

Thing is though, that loss of mass is nearly infinitesimally small in comparison to the Sun's overall mass (consider, it's been losing mass like that for billions of years, and billions of years from now it's STILL going to be losing mass). We're talking about a water balloon here with one incredibly small leak in comparison to its size. And, just as the math'll tell ya, the Sun's change in speed due to that fact is going to be equally tiny, all but unnoticeable.

So yeah, the Sun's speed, and mass, and momentum, ARE changing. But it's no more noticeable than the Sun's *drop* in mass compared to it's enormous *overall* mass.

Picture a lead bowling ball rolling down an ally. Every ten feet a piece of the bowling ball the size of a half a grain of sand flies off it. You know, and I know, that under those conditions the mass and therefore the momentum of the lead bowling ball is changing. But how noticable is that change? Not very. What's being lost is too small in comparison to the total mass of the bowling ball, so you see very little change in the bowling ball's mass and momentum. The change IS there, it's just a very tiny change.

That make more sense?
 
Last edited:

1. What is momentum?

Momentum is a measure of an object's mass and velocity. It is a vector quantity, meaning it has both magnitude and direction. In simple terms, it is the amount of motion an object has.

2. How is momentum related to energy?

Momentum and energy are related through the concept of work. Work is defined as the force applied to an object multiplied by the distance it moves. Since momentum is a measure of an object's motion, it is also related to the amount of work that is done on the object.

3. Does all forms of energy have momentum?

Yes, all forms of energy have momentum. This is because momentum is a property of an object's motion and all forms of energy involve some kind of motion, whether it is the movement of particles or waves.

4. How is the momentum of an object affected by changes in energy?

Changes in energy can affect the momentum of an object. For example, if an object gains energy, its velocity will increase, resulting in a greater momentum. On the other hand, if an object loses energy, its velocity will decrease, resulting in a smaller momentum.

5. Is there a formula for calculating the momentum of an object?

Yes, the formula for calculating momentum is: p = m * v, where p is momentum, m is mass, and v is velocity. This formula can be used to calculate the momentum of any object, as long as its mass and velocity are known.

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