On impact, the pain an airsoft pellet causes is directly related with the kinetic energy it has. This energy is directly proportional to its mass and the square of its velocity. It is important to note that doubling the velocity of a pellet will quadruple its kinetic energy. As a reference value, a 0.20 gram pellet traveling at 100 metres per second (328 ft/s) has one joule of kinetic energy. Airsoft is legal in most parts of the world. Some countries have specific restrictions, such as maximum muzzle velocity and "unrealistic" colouring to distinguish them from actual fi****ms.