Mach number

In fluid dynamics, the Mach number (M or Ma) (/mɑːx/; German: [maχ]) is a dimensionless quantity representing the ratio of flow velocity past a boundary to the local speed of sound.

where

The local speed of sound, and thereby the Mach number, depends on the condition of the surrounding medium, in particular the temperature and pressure. The Mach number is primarily used to determine the approximation with which a flow can be treated as an incompressible flow. The medium can be a gas or a liquid. The boundary can be traveling in the medium, or it can be stationary while the medium flows along it, or they can both be moving, with different velocities: what matters is their relative velocity with respect to each other. The boundary can be the boundary of an object immersed in the medium, or of a channel such as a nozzle, diffusers or wind tunnels chaneling the medium. As the Mach number is defined as the ratio of two speeds, it is a dimensionless number. If M < 0.2–0.3 and the flow is quasi-steady and isothermal, compressibility effects will be small and a simplified incompressible flow equations can be used.

Mach 2 (film)

Mach 2 is a 2001 action/drama film directed by Fred Olen Ray. It was the first film to feature the airliner Concorde being hijacked by terrorists.

Plot

Stuart Davis (David Hedison), running against the Vice-President, plans a trip to the Balkans to negotiate the release of American servicemen being held hostage by terrorists. Before he leaves, he receives a disk documenting evidence that the Vice-President has been trying to revive the American economy by causing a war in the Balkans. He announces his plans at Washington Dulles International Airport to show it to both sides in the hopes of ending the situation. He boards Concorde flight 209 to Paris along with some Air Force Officers and news employees. Unexpected Secret Service agents turn up and board the Concorde. After takeoff, the secret service agents led by Barry Rogers (Michael Dorn) shoot an Air Force officer and his men hijack the Concorde in mid-flight. Rogers takes Stuart Davis and the others hostage and forces him to hand over the disk in order to prevent the war being averted. In the cockpit, Rogers announces to the Dulles International Airport air traffic controller that the agents are armed with a nuclear device and threaten to crash the Concorde into Paris.