Are there conflicting gravities?

Question

Can the gravitational pull of the sun be measured on Earth's surface? i.e. Could a person jump higher (theoretically) in the day, because some of Earth's gravitational pull is offset by the gravitational pull of the sun? Also, if the earth's gravitational pull against the moon is enough to create a bulge in the earth (tides) then why doesn't it have more effect on people on Earth's surface?

Answer 1

" Can a person jump higher on the sun side of earth because the earth's pull is offset by the sun's gravitational pull?"

Richard, this is a common misconception (as evidenced by the previous posters answers)...but not for the reason you may think. BEAR WITH ME ON THIS LENGTHY POST .

1st, you ARE slightly lighter on the sun side of earth, but NOT because of offsetting gravity of the sun. If that were true, then on the dark side of earth you should weigh MORE because of the addition of the two gravities.
However, that is NOT TRUE , you actually also weigh slightly LESS when standing on the dark side.

Why? To get the correct astro-physics perspective you must realize that the earth AND EVERYTHING ON IT is in 'FREE FALL' around the sun.

If the center of earth and you were at the SAME distance from the sun, both would free fall toward the sun at the same rate; BUT when you are on the sun side of earth surface you are slightly closer to the sun than the center of the earth is....so you have a tiny bit more acceleration toward the sun than the earth ...thus you pull away from earth surface (and weigh less). That is the reason.

HOWEVER, standing ON THE DARK SIDE of earth, you are FARTHER from the sun than the earth is,... so you accelerate LESS than the earth toward the sun...and the earth pulls away from you slightly and YOU WEIGH LESS....NOT more (as you'd expect if adding the two gravities).

Remember...the two gravities do NOT add and subtract as you expect BECAUSE you and the earth are BOTH in free fall around the sun.

Answer 2

>Can the gravitational pull of the sun be measured on Earth's >surface? i.e. Could a person jump higher (theoretically) in >the day, because some of Earth's gravitational pull is offset >by the gravitational pull of the sun?

Yep. The pull of the sun also distorts the shape of the land, as well as water.

>Also, if the earth's gravitational pull against the moon is >enough to create a bulge in the earth (tides) then why >doesn't it have more effect on people on Earth's surface?

Dunno. Instruments can detect a lot of phenomena that we cannot feel with our senses. I feel about as heavy in an airplane as I do on the ground, and there's a difference of several miles there. Nor can I feel the mass of a mountain pulling me sideways. Both of these can be detected by a gravimeter, but not by me.

I suppose that if a strong sense of gravity had been useful to our survival, we would have evolved one. Apparently it isn't.

A later comment on an earlier answer: the period of excitation provided by the movement of sun and moon on tides has some effect, but it's not the primary effect. For example, the Mediterranean is precisely the wrong shape for the rotation of the earth to cause tidal sloshing, and so even though it is big, it has no tides. The Bay of Fundy, on the other hand, is precisely tuned to the period of the sun and moon, and thus it has very high tides. I think the big oceans are somewhere in between.

Answer 3

In answer to your question about jumping higher at noon than at midnight, the answer is yes. Now wait a minute, the difference would be so small, that you probably could not measure it. The sun is very far away, and you are very small in comparison to the sun, so your jump difference would only be infinitesimally minuscule.

The moon affects the tides mainly because it is cyclic. Imagine when you are on a swing. Every time that you swing back, your friend gives you a little push. The push just has to be greater than the forces of air resistance and friction to build up and cause you to go higher and higher. The push has to be at just the right time. This is why the tides react the way they do, the moon exerts its small force at exactly the right time because of the rotation of the earth, so the tides sway east and west in a regular motion.

Hope this helps,
Lorax

Answer 4

Yes it can but the strength of the suns gravitational force is very faint over the distance and is vastly overwhelmed by the gravitation of the Earth and the Moon.
People and other loose objects are hardly effected by the moons gravity because as you point out it produces a tidal bulge which puts more of the Earth below you so that the Earth gravitation at that point is stronger.
The centre of gravity of the Earth-Moon system is below the Earths surface.

Answer 5

Yes, these are all accurate.

However, the amount of variation in jumps by a human is probably significantly larger than the difference you'd see when the Sun and Moon were in or out of alignment with your jump.

The reason is that the Earth's gravity is 9.81 m/s^2 on the surface of the Earth, while the Moon's gravity on the surface of the Earth is about 0.000033 m/s^2. The Moon's smaller mass and further distance make its gravity much less significant than that of the Earth. It's a similar situation with the Sun.

Answer 6

how do you know it doesn't affect us? you lived here without the moon before?