Gravity model come from the fact that the nonlinear equation 1 resembles Newton’s law of gravity: export are directly proportional to the exporting and importing countries economic “mass” (GDP), and inversely proportional to the distance between them. In other words, gravity says that we expect larger country pairs to trade more, but we expect countries that are further apart to trade less, perhaps because transport costs between are higher. The gravity equation can be derived from three different trade models that assume product specialization: Ricardian models; Hecksher–Ohlin (H–O) models and increasing returns to scale (IRS) models.