Gravity is one of those things we take completely for granted. And there are two things about it that we take for granted: the fact that it is always there, and the fact that it never changes. If the Earth's gravity were ever to change significantly, it would have a huge effect on nearly everything because so many things are designed around the current state of gravity.
Photo courtesy of Zero Gravity Corporation
Eating small pieces of candy might be a problem if there was no gravity on Earth.
Before looking at changes in gravity however, it is helpful to first understand what gravity is. Gravity is an attractive force between any two atoms. Let's say you take two golf balls and place them on a table. There will be an incredibly slight gravitational attraction between the atoms in those two golf balls. If you use two massive pieces of lead and some amazingly precise instruments, you can actually measure an infinitesimal attraction between them. It is only when you get an gigantic number of atoms together, as in the case of the planet Earth, that the force of gravitational attraction is significant.
Famed Physicist, Stephen Hawking, took air travel to new heights as he left gravity and his wheel chair, floating weightless in a specially-designed jet that dives through the sky to give passengers an experience of zero gravity. The 65-year-old British physicist has been wheelchair-bound for almost 40 years.
Watch this video featuring BMX superstar Chad Kagy as he talks about gravity on HowStuffWorks. Even when Chad Kagy is spinning off the top of the half-pipe, he's stable and completely in control. Whether your launching pad is the half pipe, or the Kennedy Space Center, you HAVE to stay stable. See how NASA and Chad explain how gravity works in this video from NASA.
The reason why gravity on Earth never changes is because the mass of the Earth never changes. The only way to suddenly change the gravity on Earth would be to change the mass of the planet. A change in mass great enough to result in a change in gravity isn't going to happen anytime soon.