| MadSci Network: Astronomy |
Hi Nely, The Earth has a strong gravitational pull because it has a lot of mass. Every object which has mass, which is pretty much everything except light (photons) and a few exotic particles, attracts every other object which has mass. This attraction is called gravity, and the more massive the object the stronger its gravitational pull. Since the Earth is very big, its gravitational pull is very strong, at least compared to everyday objects like baseballs and people. The gravitational force between two objects also gets stronger as you bring them closer together, so even though the Sun is *much* more massive than the Earth, we don't feel as much gravitational pull from it as we do from the Earth. You're very close to the Earth (only about 4000 miles from its center) and about 93 million miles away from the Sun. Henry Cavendish actually measured the very small gravitational force between two small masses, in 1798. Tom Henderson of Glenbrook South High School has a very nice web page about gravity, which includes a description of Cavendish's experiment, at http://www.glenbrook.k12.il.us/gbssci/phys/Class/circles/u6l3d.html . I hope this helps. Please feel free to E-mail me (stevenlevin@we.mediaone.net) if you have more questions about this. Steve Levin __________________________________________________________ DISCLAIMER: Just because I work for JPL/NASA/Caltech doesn't mean anything I say is in any way official. This is just me talking, not NASA, JPL, or Caltech.
Try the links in the MadSci Library for more information on Astronomy.