# Is there anything with a constant weight?

1. Feb 27, 2014

### jmiller0921

Is there any particle in physics that has a constant weight regardless of the environment it is in, with respect to gravity? something like light, roughly 300000000m/s always, but in terms of weight instead of speed. Everything that I have seen at this point is always relative to something its next to or something to that effect. I'm looking for something that is always the same weight with respect to gravity. I was thinking a light photon would be , from what I've seen this varies.

2. Feb 27, 2014

### dauto

weight is given by an object's mass times the local gravitational acceleration. Since the local gravitational acceleration varies from place to place, the object's weight must change from place to place. I get the feeling that's not what you intended to ask. But that's the answer to the question you asked.

3. Feb 27, 2014

### jmiller0921

What I mean is, is there anything that has a constant mass that would also have a constant weight with respect to gravity? It seems like there could be something that was always the same mass when it is observed. from what I've read everything varies in mass and weight. Im looking for something that is always the same no mater what.

4. Feb 27, 2014

### Staff: Mentor

No, mass is a physical property of an object and does not change. Only weight changes.

5. Feb 27, 2014

### ZapperZ

Staff Emeritus
What you are asking is this: I have this apple. Is there a place where price of this apple will always remain the same, no matter where I go and how long I have it?

Now see if you can understand the responses that you have been given.

Zz.

6. Feb 27, 2014

### bland

Light does not have a constant speed regardless of environment. It travels slower in water than in air and slower in air than in intergalactic space.

7. Feb 28, 2014

### csleong

Make it simple, weight = mass x gravity, gravity is not a constant but mass remains the same, you know weight will change proportion to local gravity.

8. Feb 28, 2014

### llstanfield

Weight is directly dependent on the mass of X and the gravitational body of something even more massive. To technically answer your question, everyone on this planet has a constant weight, to some degree. So, your weight is directly dependent on the force of G. Therefore, I don't think there exists a 'constant' weight.

When you start talking about particles of light (which may not be an accurate description), the particles or sometimes waves, don't have weight; because particles that small are not observed to be directly affected by gravitational forces.

9. Feb 28, 2014

Not necessarily.

10. Feb 28, 2014

### llstanfield

Care to elaborate on my mistake? Really interested. Thanks.

11. Feb 28, 2014

### ZapperZ

Staff Emeritus
You can feel "weight" when you are accelerating "upwards", with no need of the presence of another large body to generate the effect of gravity.

Zz.

12. Feb 28, 2014

However,weight of an object is usually taken to be the force on the object due to gravity.

It doesn't have to be possessing more gravity than the mass of X.
Weight of me in terms of earth is 600N.
Weight of earth in terms of me is $m_2a$.
Find $a$ using $F=\frac{Gm_1m_2}{r^2}$

13. Feb 28, 2014

### llstanfield

Oh I see. Please correct me if I'm wrong, but is this effect related to Einstein's theory of general relativity? Now that I think about it, maybe I was wrong by saying the effect of weight was necessary of having a greater massive object force. But, perhaps it's more dependent on the mass times the acceleration on any interacting body? For instance, even in an elevator or rocket ship given this force, aren't those two things much more massive than the obvious body that's being exerted on? I mean, can you provide me any other example where something with less mass of a heavier one determines the weight? Thanks for your time.

Last edited: Feb 28, 2014
14. Feb 28, 2014

### llstanfield

Oh okay, and you are absolutely right. That's what I intended to say, as in the mass of an object related to weight, is subject to the gravitational force....so, you or I, would weigh much more on Jupiter or the Sun for instance. I understand the simple equation of F=mxg, but can you explain the equation that you have given? As far as telling me what r squared and Gm1 stands for? Thanks for your contribution and feedback. Much appreciated.

15. Feb 28, 2014

### jmiller0921

"What you are asking is this: I have this apple. Is there a place where price of this apple will always remain the same, no matter where I go and how long I have it?

Now see if you can understand the responses that you have been given.

Zz."

yes. This is what I mean. Is there any measurable particle that is always the same mass "exactly" in vacuum? It seems to me that all particles have variable sizes and eventually some decay into other particles. Im looking for something that is stable and always has the same mass (no variance) in vacuum.

16. Feb 28, 2014

$F=\frac{Gm_1m_2}{r^2}$ is the Universal Law of Gravitation

F is the force.
G is the Universal Gravitational Constant.

$m_1$ is the mass of you or me.(In my example)
$m_2$ is the mass of Earth (In my example given)
$r$ is the distance between the center of mass of earth and you.

Let your mass be 100kg :rofl:
Let the mass of earth be $5.97219 × 10^{24}$kg.
You stand 1m away from earth.
$F=m_1a=\frac{Gm_1m_2}{r^2}$
Simplifying gives,
$a=\frac{Gm_2}{r^2}$ - where a is the acceleration of you.
Again do the same with m_2
$a=\frac{Gm_1}{r^2}$ where a is the acceleration of earth.
So Weight =mass x acceleration.
Find the weight of Earth and you yourself.

Last edited: Feb 28, 2014
17. Feb 28, 2014

### llstanfield

I have a BA in Sociology. However, physics has just recently grabbed my attention, which is why I asked for that elementary understanding of the equation, and respond to the original post to the best of my ability. I signed up on this site to give my understanding of the subject, and ask questions about it in order to learn more.

18. Feb 28, 2014

You are welcome here.
It's actually not very elementary.I'll study it at A-level. However,I know how it works.

19. Feb 28, 2014

### ZapperZ

Staff Emeritus
But that isn't what you asked originally, is it?

We know about "mass". A look in the Particle Data Book confirms that there ARE plenty of elementary particles with unambiguous mass that we can clearly define. These do not change, or else we will never be able to identify them.

Note that in my example, the apple did not change!. Its value may, but the apple itself hasn't.

Zz.

20. Feb 28, 2014

### llstanfield

I appreciate that and this site. And I will definitely refer to you in the future. But for a layman, attempting to understand these complicated physical questions, the equation that you've recently posted in my opinion, is "elementary' or a Newtonian understanding of the world. For instance, regarding the original post, I'm not sure how much a particle would 'weigh' in a vacuum. Because that level of physics transcends classical physics in my opinion.