of energy (in the Bernoulli equation for an incompressible fluid this term represents work of pressure forces). Head is useful in specifying centrifugal pumps because their pumping characteristics tend to be independent of the fluid's density.

There are four types of head used to calculate the total head in and out of a pump:
Velocity head is due to the bulk motion of a fluid (kinetic energy). Its pressure head correspondent is the dynamic pressure.
Elevation head is due to the fluid's weight, the gravitational force acting on a column of fluid.
Pressure head is due to the static pressure, the internal molecular motion of a fluid that exerts a force on its container.
Resistance head (or friction head or Head Loss) is due to the frictional forces acting against a fluid's motioncondemned the inclusion of Crimea, saying in an online statement : "Coca-Cola's actions violate the official US position condemning Russia's illegal occupation of Crimea, which is and has always been an integral part of Ukraine."

image copyright Twitter image caption Many Ukrainians called for a boycott of the company

Coca-Cola posted the original message on VK, Russia's biggest social network, on 30 December, with the caption: "Celebrate winter holidays from Moscow to Vladivostok."

Following condemnation from Russians, it republished the image to include Crimea and went further, including the Kuril Islands - seized by Russia shortly before Japan's surrender in World War Two in 1945 - and Kaliningrad, a Russian exclave annexed from Germany in the same year.

Map blunders

In 2011, a Chinese firm came under fire for drawing up a map