Gravity is caused by mass. Everything causes gravity but the bigger it is and more mass it has the more pull is felt by its gravity. So you are pulling the earth towards you and the earth is pulling you. The earth is much bigger and has more mass, so it pulls much more. Gravity gets weaker the further away you get from its source.
The earths crust does not have the same mass all over, so some areas have slightly less gravity than others. The differences between areas are very very small.
The moon has only a quarter the mass of the earth, so gravity on the moon is a quarter of earths gravity.
Not sure what you mean by "change gravity"; a nebula has mass, therefore it exerts a gravitational force.
gravity can change the motion of an object because of magic
weight
Yes. As acceleration due to gravity increases so does the object's weight. The reverse is true when gravity decreases. Mass, however, does NOT change with gravity.
No, it gives you weight. Mass does not change in the presence of gravity.
As compared to Earth, you mean? If an object doesn't change its shape, the center of mass doesn't depend on gravity - and the center of gravity hardly does so.
no
yes
Air has no effect on gravity. But the presence of air can change the response of an object to the force of gravity alone.
Yes. Weight is directly proportional to the force of gravity.
Yes. What you weigh depends on the gravity of the planet you are on.
the air pressure is different where if the gravity substances were to change it will be normal