If it wasn’t for the Earth’s gravity, we’d all float off into space. So don’t panic when I tell you that you’re constantly falling towards the Earth at an accelerating rate of 9.8 meters/second2. Fortunately, you’re also standing on the Earth, so that’s keeping you from falling.
Gravity comes from mass. The more mass an object has, the more gravity it will exert on objects around it. The amount of gravity that you experience falls off quickly over distance. So, the force of gravity that you feel on the surface of the Earth is much different from what you would experience at the distance of the Moon, or further. 9.8 m/s2 is the gravity close to the surface.
You might be surprised to know that the force of gravity on Earth actually changes depending on where you’re standing on it. The first reason is because the Earth is rotating. This rotation is trying to spin you off into space, but don’t worry, this force isn’t much. The gravity of Earth at the equator is 9.789 m/s2, while the force of gravity at the poles is 9.832 m/s2. In other words, you weigh more at the poles than you do at the equator because of this centripetal force.
Gravity also decreases with altitude, since you’re further away from the Earth’s center. The decrease in force from climbing to the top of a mountain is pretty minimal (0.28% less gravity at the top of Mount Everest), but if you’re up at the altitude of the International Space Station, you only experience 90% of the force of gravity you’d feel on the surface.
Finally, the force of gravity can change depending on what’s under the Earth beneath you. Higher concentrations of mass, like high density rocks can change the force of gravity that you feel; although, this amount is very slight. NASA missions have mapped the Earth’s gravity field with incredible accuracy.
We have written many articles about the Earth for Universe Today. Here’s an article about detailed gravity maps of Earth.
We have also recorded an episode of Astronomy Cast about Earth, as part of our tour through the Solar System – Episode 51: Earth.