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Velocity is a physical vector quantity: both magnitude and direction are needed to define it. The scalar absolute value of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s or m⋅s −1). For example, "5 metres per second" is a scalar, whereas "5 metres per ...
If so, for consistency, the speeds of navigational fluids (ocean currents, tidal streams, river currents and wind speeds) are also measured in knots. Thus, speed over the ground (SOG; ground speed (GS) in aircraft) and rate of progress towards a distant point ("velocity made good", VMG) can also be given in knots.
Speed is the magnitude of velocity (a vector), which indicates additionally the direction of motion. Speed has the dimensions of distance divided by time. The SI unit of speed is the metre per second (m/s), but the most common unit of speed in everyday usage is the kilometre per hour (km/h) or, in the US and the UK, miles per hour (mph).
The metre per second is the unit of both speed (a scalar quantity) and velocity (a vector quantity, which has direction and magnitude) in the International System of Units (SI), equal to the speed of a body covering a distance of one metre in a time of one second.
The relative velocity of an object B relative to an observer A, denoted (also or ), is the velocity vector of B measured in the rest frame of A. The relative speed v B ∣ A = ‖ v B ∣ A ‖ {\displaystyle v_{B\mid A}=\|\mathbf {v} _{B\mid A}\|} is the vector norm of the relative velocity.
If is measured in radians, the arc-length from the positive x-axis around the circle to the particle is =, and the linear velocity is () = = (), so that =. In the general case of a particle moving in the plane, the orbital angular velocity is the rate at which the position vector relative to a chosen origin "sweeps out" angle.
The category identifies units of speed or velocity. Pages in category "Units of velocity" The following 12 pages are in this category, out of 12 total.
Indicated airspeed is a better measure of power required and lift available than true airspeed. Therefore, IAS is used for controlling the aircraft during taxiing, takeoff, climb, descent, approach or landing. Target speeds for best rate of climb, best range, and best endurance are given in terms of indicated speed.