# Weight at noon & at night !

1. Jan 9, 2008

### ayan_dg

At noon when Sun is directly over my head, the gravitational pull of Earth & Sun on me are in opposite direction but during night as the Earth is between me & Sun , the attraction of Earth & Sun are in the same direction. So at night my weight should be more than in noon. But it does not happen actually. Please explain why ?

2. Jan 9, 2008

### dst

The difference in weight is most likely negligible but you would expect it to be there. I hear you gain 2cm of height in the daytime until you sleep again.

3. Jan 9, 2008

### mda

As stated above, gravitational changes are neglible (relative change is 6x10^-4).
Far more significant is the change in mass due to flow of food and especially water.

4. Jan 9, 2008

### Janus

Staff Emeritus
First off, your premise is flawed. You would not expect to weigh more at night. Any effect the Sun has on your weight would be due to tidal forces, and for the same reason we have two tidal bulges, the tendancy would be to weigh less at noon and midnight, and more at sunrise and sunset.

Secondly, as already mentioned, the Sun's effect on your weight is tiny.

5. Jan 9, 2008

### pixel01

Although tiny, in astrology, when a man was born, day or night may have some effect, I ve heard.

6. Jan 9, 2008

### jobyts

Is astrology based on science?

7. Jan 9, 2008

### pixel01

Some astrologists claim so. I am not sure. Can you prove that astrology is not based on science?

8. Jan 9, 2008

### dst

The methodology:

Science - Observation => Hypothesis => Controlled Observation => Conclusion
Astrology - Conclusion = Hypothesis =/= Observation

9. Jan 9, 2008

### G01

If astrology was based off of science, we would expect the predictions of astrology to be correct most of the time, since for them to be scientific, they would have to be based off of evidence.

So, astrology is not scientific since the conclusions are made without any evidence, (There is no hard evidence that the stars affect our lives.) and the conclusions do not correspond with observation. (The predictions are not always correct. If they are correct, it is not with enough regularity to assume anything other than luck as the cause.)

10. Jan 9, 2008

### wysard

First off, your weight does in fact change, you are not imaging it.

Second: The difference is tiny. Easy to calculate, but tiny. Remember, the Moon moves the tides, not the Sun. Not because the Sun does not create an effect, but because it is swamped by the larger gravitational effects of the Moon.

Remember, the gravity effects of one body on another are proportional to the distances. So while the Sun is Really, REALLY big, it is so far away that unless you have a planetary mass, the effect on you is almost non-existant compared to say the mass of the moon which is trivial by comparison but because it is so much closer the effect is vastly (if still tiny) larger.

When in doubt, check your local tide charts. At Neap tide you weigh a tiny amount less, and at Ebb tide you weigh a tiny amount more.

11. Jan 14, 2008

### puopg

Heres Why: I believe this is correct, not fully sure though.

Contrary to what someone here said about your weight, weight is not determined by the force YOU push down on the scale. Rather, it is the force the SCALE pushes up on you. That said, think of the problem. You have earth. You have the sun at the center. The sun pulls you toward itself. simple right? so now u have a force going up (assuming you picture this as the sun above the earth). When you weigh yourself during the day, the scale pushes up as well. So you can mathematically add the forces together to get one value. Now think at night. Instead, you have the force of the sun pulling up, but the force the scale does on you goes DOWN. Thus you weigh less during the night than at day. It would help to have an actual physics instructor here to check our work.

12. Jan 14, 2008

### puopg

False

FALSE, remember the CONSERVATION OF MASS = the mass of a closed system remains CONSTANT no matter what processes are occurring inside that system.

13. Jan 14, 2008

### puopg

What this person is trying to use is the relationship between Force of gravity between two bodies. This is known as F = G (constant) m(body 1) x m(body2) / (distance between the two centers of mass ) Squared. simply seen as F = Gm1m2/ r^2. If you look at it this way, you would think that the farther a body is away, the less force gravity has on it. Logical right? but, in this situation, we need to realize that your weight is not how much u push on that darn scale. it's how much it pushes up on you. so you look for the situation that maximizes the force in the same direction.

14. Jan 14, 2008

### mda

The human body is not a closed system... think about it.

15. Jan 14, 2008

### nanoWatt

If you think the sun is big, take a look at these other stars:

Last edited by a moderator: Sep 25, 2014