The ideal gas law is an excellent example of a model, in terms of both their usefulness and imperfections. It states that, within any particular volume of a gas at a particular temperature and pressure, the number of gas molecules or atoms can be exactly calculated, regardless of the actual composition of the gas involved. However, it is called the ideal gas law for a reason. It assumes uniform conditions throughout the given volume of gas, a condition that can almost never actually be met. Bodies of gases in the real world, even within sealed containers, have variations in temperature and pressure, along with accompanying currents. Similarly, the equation for the volume of a sphere gives a good approximation for the volume of roughly spherical objects, but no perfect spheres are likely to exist in actual nature.