Is the Earth's gravity a constant force?

There are a lot of people who are aware that the reason why we can walk on land is because of gravity. This is said to be a constant thing, but even if it is constant, this can still change depending on some factors such as altitude. Your distance from the center of the earth will always play a huge difference in how strong the gravitational pull is going to be.

In space, there is not enough gravity. This explains why those who have tried to go to the moon can barely walk on the moon because of the lack of gravity available there. Weight can also make a difference in how fast an item is going to fall to the ground.