# PHYS 1111L Lecture Notes - Lecture 5: Si Base Unit, Kinematics

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VELOCITY

The velocity of an object is the rate of change of its position with respect to a frame of

reference, and is a function of time. Velocity is equivalent to a specification of its speed and

direction of motion (e.g. 60 km/h to the north). Velocity is an important concept in

kinematics, the branch of classical mechanics that describes the motion of bodies.

Velocity is a physical vector quantity; both magnitude and direction are needed to define it.

The scalar absolute value (magnitude) 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

as the SI base unit of (m⋅s−1). For example, "5 metres per second" is a scalar, whereas "5

metres per second east" is a vector. If there is a change in speed, direction or both, then

the object has a changing velocity and is said to be undergoing an acceleration.

-ZeonGrooza

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