Gravity is the force of attraction between all masses. Although gravity is said to be exerted by everything that has a mass, only those objects with very large masses actually affect anything near them. A gravitational field is the area around the body that is exerting the gravitational pull. It can be defined as the gravitational force felt by a unit's mass placed at a point in space.
Gravity has three very important effects. First, it makes all things accelerate towards it. On Earth, acceleration due to gravity is 9.8 meters per second squared. That means that no matter what is falling towards Earth, it will do so with the same acceleration, unless air resistance is taken into account.
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Second, gravity gives everything weight. Weight is the force of gravity pulling something toward the Earth. Mass and weight are not the same thing, and mass is used to determine the weight of something. The mass of an object is always the same, but its weight can change based on the strength of the gravitational field. For example, the mass of an object would be the same on the moon as it was on Earth, but its weight would be different due to the different gravitational forces.
Finally, gravity keeps all objects in the solar system in their orbits. An orbit is caused by the balance of the forward motion of the object and the force of gravity pulling it inwards. For example, the orbit of the Earth around the Sun is due to the forward motion of the Earth and the Sun’s gravitational pull on it. The same happens with the moon around the Earth.
The closer one object is to another, the stronger the gravitational field. In the Solar System, planets that are closer to the Sun have a much stronger force of attraction acting on them. To counteract this attraction, they must move around the Sun a lot quicker. A gravitational field decreases very quickly with distance.
The size of the force of gravity follows an inverse square relationship. If the gravity of an object were measured and then it was moved twice as far away from the large object causing the gravitational field, the force of gravity would be reduced by a factor of four. It if were moved three times as far away, the gravitational force would be reduced by a factor of nine, or the square of three. The opposite can be said if the object were moved closer as well, except gravity would be increased instead of being reduced.