Thread: Earth-Moon Barycentre

If the earth and the moon orbit the barycenter that is a few thousand kilometers under the earths surface pointing towards the moon at all times then my question is this:

Why are all objects on earth pulled down towards the centre of the earth? And not the barycenter? Is there a difference between orbital gravity and gravity in general? Or am I confusing this with something else.

Thanks guys! :-)

Use the gravitational formula, and you will see that for someone on the surface, the earth's mass is almost all of the gravity. Technically, you do weigh a hair less when the moon is overhead, but the amount is extremely small, too small to easily measure.

Originally Posted by Quantime

If the earth and the moon orbit the barycenter that is a few thousand kilometers under the earths surface pointing towards the moon at all times then my question is this:

Why are all objects on earth pulled down towards the centre of the earth? And not the barycenter? Is there a difference between orbital gravity and gravity in general? Or am I confusing this with something else.

Thanks guys! :-)

The barycenter is the "balance point" between the Earth and Moon. One way to look at it is that if the Earth and Moon were sitting on a see-saw, the barycenter is where you would have to put the fulcrum is order for them to balance. While for something that is far removed from the Earth-moon system (like the Sun) it behaves like the gravitational center of the Earth-Moon system, once you get closer in, the "lumpiness" of the system caused by the fact that the Earth and Moon are separate masses begins to dominate.

Thank you very much guys very clear