Gravity of Earth

The gravity of Earth, denoted by g, is the force that pulls objects toward the center of our planet. This happens because of the mass inside Earth and the spinning motion of our world. Gravity is a pull that makes things fall down and gives weight to everything around us.

In science, we measure this pull using units called metres per second squared (m/s²). Near the surface of Earth, this pull is about 9.8 m/s². This means if you drop something, it will go faster and faster by about 9.8 metres every second.

The strength of Earth's gravity can change a little bit depending on where you are. Scientists use a standard value of 9.80665 m⋅s⁻² for many calculations. This value was chosen a long time ago and helps us understand how much things weigh in different places.

Weight is the force of gravity pulling on an object. It depends on both the mass of the object and how strong gravity is. While most of the gravity we feel comes from Earth itself, other forces like Earth's spin also play a small role in how heavy things seem.

Magnitude

The Earth’s gravity, or the pull it has on objects, changes a little depending on where you are. This is because the Earth isn’t a perfect sphere. It is a bit squashed at the poles and bulges at the equator. The Earth’s spin also makes things feel a little lighter near the equator.

Gravity is weakest on tall mountains, like Nevado Huascarán in Peru, and strongest at the poles. In cities, gravity is usually close to 9.8 metres per second squared. Scientists use a standard value of 9.80665 metres per second squared when an exact local measurement isn’t needed.

Because the Earth spins, places near the equator feel a tiny bit lighter compared to the poles. The farther you are from Earth’s center—like when you’re on a mountain—the weaker gravity feels. Even astronauts in space still feel almost all of Earth’s gravity, but they seem weightless because they’re constantly falling around the Earth.

Atmosphere

The strength of gravity on Earth helps create and keep our atmosphere. This is important for having water in our oceans. Gravity works against the energy from the Sun that moves gas molecules. Earth's gravity is not too strong, so light gases like hydrogen can escape, but it is strong enough to hold onto bigger molecules. This balance also helps create weather as the Earth gets different amounts of heat.

Direction

Main article: Vertical direction

Gravity is a force that has both strength and direction. If the Earth were a perfect sphere, gravity would always point straight down toward the center. But the Earth is slightly flattened, so gravity doesn’t always point exactly toward the center. There are also very small changes in gravity’s direction caused by things like mountains.

Comparative values worldwide

Gravity changes depending on where you are in the world. Places closer to the poles, like Anchorage and Helsinki, have slightly stronger gravity—about 0.5% more—than cities near the equator, such as Kuala Lumpur. Gravity also changes with height above sea level. For example, Mexico City, which is high up, has lower gravity than cities at lower elevations like Washington, D.C.. You can find exact measurements in special reference books.

Mathematical models

Main article: Theoretical gravity

Gravity on Earth changes a little bit depending on where you are. Scientists use special math to learn how strong gravity is in different places. One formula shows how gravity changes based on how far north or south you are from the equator. Another formula, called the WGS-84 Ellipsoidal Gravity Formula, uses the shape of the Earth to make these calculations more exact. These formulas help scientists and engineers learn about gravity all over Earth.

Estimating g from the law of universal gravitation

From the law of universal gravitation, we can learn how Earth's gravity pulls on objects. This law shows that the force pulling an object toward Earth depends on the mass of the Earth and the distance from its center.

Using another idea from physics called Newton's second law, we can link this force to the acceleration we call gravity. By comparing these ideas, we find a simple way to calculate gravity's strength. If we know the gravitational constant, Earth's mass, and Earth's radius, we can estimate gravity's effect at Earth's surface. This calculation gives us a value close to what we measure, though Earth isn't a perfect sphere and rotates, which causes small differences.

Measurement

Main article: Gravimetry

The measurement of Earth's gravity is called gravimetry. Scientists use special tools and satellites to find out how strong gravity is in different places on Earth.