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The study of motion and of physical concepts such as force and mass is called dynamics.



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The part of dynamics that describes motion without regard to its causes is called kinematics.



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A frame of reference is a choice of coordinate axes that defines the starting point for measuring any quantity, an essential first step in solving virtually any problems in mechanics. 


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The displacement Δx of an object is defined as its change in position, and is given by Δx = x_{f}  x_{i} where the initial position of the object is labeled x_{i }and the final position is x_{f}.



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In general, a vector quantity is characterized by having both a magnitude and a direction.



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A scalar quantity has a magnitude, but no direction.



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The average speed of an object over a given time interval is deﬁned as the total distance traveled divided by the total time elapsed [image] 


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The average velocity [image] during a time interval [image] is the displacement [image] divided by [image] [image]



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The average velocity of an object during the time interval [image] is equal to the slope of the straight line joining the initial and final points on a graph of the object's position versus time. 


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The instanteneous velocity [image] is the limit of the average velocity as the time interval [image] becomes infinitesimally small [image] 


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The slope of the line tangent to the position vs. time curve at A is defined to be the instantaneous velocity at that time. 


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The instantaneous speed of an object, which is a scalar quantity, is defined as the magnitude of the instantaneous velocity.



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Definition
The average acceleration [image] during the time interval [image] is the change in velocity [image] divided by [image] [image]


