Gravity: The Elements of Geodesy # Gravity ## Global Positioning Tutorial Imagine if all of the Earth topography, mountains and valleys were scoured off leaving a continuous world's ocean completely at rest, without the effects of currents, weather and tides. The effect of the Earth's gravity on this hypothetical world mean sea level is represented by the geoid. However, because the Earth's gravity is not equal in all places, this hypothetical ocean is not perfectly smooth. The strength of the Earths' gravity, and consequent effect on the shape of the geoid is represented by color variations in this image. Gravity is the force that pulls all objects in the universe toward each other. On Earth, gravity pulls all objects "downward" toward the center of the planet. According to Sir Isaac Newton's Universal Law of Gravitation, the gravitational attraction between two bodies is stronger when the masses of the objects are greater and closer together. This rule applies to the Earth's gravitational field as well. Because the Earth rotates and its mass and density vary at different locations on the planet, gravity also varies. In this global map of the geoid (Geoid99), the area in blue

# Why does gravity act at the centre? Tags: newtonian-mechanics, forces, newtonian-gravity, symmetry - Score: 1 - Views: 1675 - Answers: 4 - Answered: yes - Asked by: user273923 - Asked: 2020-09-05 - Edited: 2020-09-05 - Site: physics - Closed: closed ## Question Why does gravity act at the centre of earth and how does that happen? ## Answers ### Answer by Philip Wood (score: 17) All parts of the Earth exert a pull on another body (such as an apple) and all parts of the Earth are pulled by external bodies (such as apples). Let's consider the pull that the Earth exerts on the apple. Imagine the Earth divided up into kilogram portions by imaginary surfaces. The portion nearest the apple will exert the greatest pull, straight downwards on the apple. The (antipodean) portion furthest away will exert the least pull, though it will still be downwards, that is towards the centre of the Earth. Portions of the Earth to the North, South, East and West of the apple and at various depths inside the Earth will also pull the apple, but not straight downwards. The vector sum of these forces is the resultant pull. Newton famously proposed the Law of Gravitation that every particle attracted

--> What Is Gravity? | NASA Space Place – NASA Science for Kids You are using an outdated browser. For a faster, safer, and more beautiful web upgrade for free today. what-is-gravity fundamental-physics What Is Gravity? Gravity is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun. What else does gravity do? Why do you land on the ground when you jump up instead of floating off into space? Why do things fall down when you throw them or drop them? The answer is gravity: an invisible force that pulls objects toward each other. Earth's gravity is what keeps you on the ground and what makes things fall. An animation of gravity at work. Albert Einstein described gravity as a curve in space that wraps around an object—such as a star or a planet. If another object is nearby, it is pulled into the curve. Image credit: NASA Anything that has mass also has gravity. Objects with more mass have more gravity. Gravity also gets weaker with distance. So, the closer objects are to each other, the stronger their gravitational pull is. Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. That's what gives you weight. And if you were on a planet with less mass than Earth, you would weigh less than you do here. Image credit: NASA You exert the same gravitational force on Earth that it does on you. But because Earth is so much more massive than you, your force doesn’t really have an effect on our planet. Gravity in our universe Gravity is what holds the planets in orbit around the sun and what keeps the moon in orbit around Earth. The gravitational pull of the moon pulls the seas towards it, causing the ocean tides. Gravity creates stars and planets by pulling together the material from which they are made. Gravity not only pulls on mass but also on light. Albert Einstein discovered this principle. If you shine a flashlight upwa

What Is Gravity? | NASA Space Place – NASA Science for Kids what-is-gravity fundamental-physics # What Is Gravity? Gravity is the force by which a planet or other body draws objects toward its center. The force of gravity keeps all of the planets in orbit around the sun. ## What else does gravity do? Why do you land on the ground when you jump up instead of floating off into space? Why do things fall down when you throw them or drop them? The answer is gravity: an invisible force that pulls objects toward each other. Earth's gravity is what keeps you on the ground and what makes things fall. An animation of gravity at work. Albert Einstein described gravity as a curve in space that wraps around an object—such as a star or a planet. If another object is nearby, it is pulled into the curve. Image credit: NASA Anything that has mass also has gravity. Objects with more mass have more gravity. Gravity also gets weaker with distance. So, the closer objects are to each other, the stronger their gravitational pull is. Earth's gravity comes from all its mass. All its mass makes a combined gravitational pull on all the mass in your body. That's what gives you weight. And if you were