On Earth's surface, the gravitational force is relatively uniform, meaning that there is very little difference in gravity between two points that are close to each other. The variation in gravity due to the Earth's shape, rotation, and local density variations is generally small and not easily perceptible.
However, when it comes to satellites orbiting around the Earth, the situation is different. Satellites remain in orbit due to the balance between their orbital velocity and the gravitational force pulling them toward Earth. The force of gravity decreases with distance, so as a satellite moves higher above the Earth's surface, the gravitational force it experiences diminishes.
This variation in gravity with altitude is the key factor that enables satellites to stay in orbit. Although the overall difference in gravity between the satellite's location and the Earth's surface is not substantial, it is sufficient to maintain the satellite in a stable orbit.
In essence, satellites are in a constant state of free fall around the Earth. Their orbital velocity and altitude are carefully calculated to ensure that they are always falling toward the Earth but also moving forward fast enough that they continually miss the planet.
It is important to note that while the gravitational force decreases with altitude, it never entirely disappears. Even at high altitudes, there is still a gravitational pull from the Earth, which keeps satellites in orbit.