Gravity
You'll fall for it!!
About gravity
Every time you jump, you experience gravity. It pulls you back down to the ground. Without gravity, you'd float off into the atmosphere -- along with all of the other matter on Earth.
You see gravity at work any time you drop a book, step on a scale or toss a ball up into the air. It's such a constant presence in our lives, we seldom marvel at the mystery of it -- but even with several well-received theories out there attempting to explain why a book falls to the ground (and at the same rate as a pebble or a couch, at that), they're still just theories. The mystery of gravity's pull is pretty much intact.
What we know about gravity
Gravity
As for the science behind the action, we know that Isaac Newton defined gravity as a force -- one that attracts all objects to all other objects. We know that Albert Einstein said gravity is a result of the curvature of space-time. These two theories are the most common and widely held (if somewhat incomplete) explanations of gravity.
Gravity
Astronauts are also experience about as much force from Earth's gravity as we are on the surface. How do they not fall down to Earth? The answer is that they are constantly falling towards the earth- but are moving so fast that they keep missing! This speed required to consistently miss the earth is called the 'escape velocity'.
Gravity
Try finding two similarly sized, but different weighted object. Hold them out one in each hand. Before you drop them, have a guess which do you think will land fist?Now drop them at exactly the same time. You might be surprised to notice that both land at the same time (any difference will be from wind resistance). The reason is a bit technical, but the laws of physics are such that the mass divides out perfectly causing all objects, regardless of mass, to accelerate at the same rate under gravitational forces. All objects on earth will accelerate down at 9.8meters per second squared.