Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) ofvelocity is called "speed", being a coherent derived unit whose quantity is measured in the SI (metric) system as metres per second (m/s) or as the SI base unit of (m⋅s−1).
In physics, tension describes the pulling force exerted by each end of a string, cable, chain, or similar one-dimensional continuous object, or by each end of a rod, truss member, or similar three dimensional object.
The kinetic theory describes a gas as a large number of submicroscopic particles (atoms or molecules), all of which are in constant, randommotion. The rapidly moving particles constantly collide with each other and with the walls of the container.