Gravity

Gravity, or gravitation, is a force that draws matter together, and is a force of attraction.  Any object that has mass applies a gravitational pull on any other object that has mass.  Objects with more mass possess more gravitational pull.  For instance, the Earth has so much mass, it holds the molecules of gas in the atmosphere close to our surface. Gravity is experienced every time you jump or drop something. Gravity is responsible for returning you to the Earth, and making an object fall.  Without gravitational pull, objects would float off into space.

Gravity exists everywhere.  The Sun’s gravity impacts the entire solar system, which keeps the planets in their orbits.  The Earth’s gravity keeps the Moon and our satellites in orbit. However, when astronauts visit space, they experience weightlessness.  They are actually falling toward the Earth, but the Earth’s curvature causes them to never reach it.  They are really falling around the Earth.  In fact, the Moon and all other objects are actually falling, being held into orbit by the Earth’s gravity.

When we think of gravity and the rates at which objects fall, we sometimes believe that objects with more mass accelerate at a higher speed than those with a lesser mass.  In fact, all objects fall at the same rate, unless they are impacted by air resistance.  If you were to compare a feather and a baseball, you might be surprised that with the absence of air (such as in a vacuum), both would fall at the same speed!

Sources:

http://www.physics4kids.com/files/motion_gravity.html

http://en.wikipedia.org/wiki/Gravity

http://www.universetoday.com/95308/why-are-astronauts-weightless-in-space/

http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-is-gravity.html

http://science.howstuffworks.com/environmental/earth/geophysics/question232.htm