Gravity model
Gravity models try to explain why two places are either close together or far apart. They help us understand the movement of things (people, goods, diseases, etc.), and why they move between some places and not others.
Gravity models use forces, just like the forces that make apples fall from a tree to the ground. When two places are close together, the force of gravity is strong and the two places are pulled together. When two places are far apart, the force of gravity is weaker and the two places are pushed apart.
Gravity models use this idea to explain why people, goods, and diseases move between places. If two places are close together, it's easy for people, goods, and diseases to move between them, similar to how an apple falls off a tree. But if two places are far apart, it's harder for people, goods and diseases to move between them—just like it's harder to make an apple move from the ground.
Gravity models use forces, just like the forces that make apples fall from a tree to the ground. When two places are close together, the force of gravity is strong and the two places are pulled together. When two places are far apart, the force of gravity is weaker and the two places are pushed apart.
Gravity models use this idea to explain why people, goods, and diseases move between places. If two places are close together, it's easy for people, goods, and diseases to move between them, similar to how an apple falls off a tree. But if two places are far apart, it's harder for people, goods and diseases to move between them—just like it's harder to make an apple move from the ground.