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182 We need to be more clear about the terms CHANGE in position, displacement ,
displacement
and distance travelled in A) 1Dimension in fixed direction , B) fixed axis
distance
fixed
fixed
or 1Dimension with CHANGE in direction and C) 2Dimensions. These terms
need to be explained from both the Calculus point of view and the Physics
(what is happening in nature) point of view and how they are related.
A) 1Dimension in fixed direction : in the example the car travelled East in a
fixed
fixed direction, that is to say moving along a straight line without reversing or
changing direction. So in this very speical case from the Physics point of view:
Physics
CHANGE in position = displacement = distance travelled .
displacement distance
Also, from the Calculus point of view, over a given interval, say [t 1 , t 2 ] :
CHANGE in position = t2 ∫ t1 x’(t)dt = area under the speed cur ve
area
curv
ar This is because the SPEED function did NOT CHANGE SIGN. In 1Dimensional motion
the SPEED function will CHANGE SIGN only if there is a CHANGE in direction.
B) fixed axis or 1Dimension with CHANGE in direction : Let us review an example
fixed
of the projected ball.
1Dimension
y(t1) y(T/ 2) y’(t1) y(t2) 0987654321
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654321 T/ 2 (0,0) t2 t1 y’(t2) T t vertical speed y ’(t) = u . s i n θ  g t
183 CHANGE in position over [t1, t2] = dispalcement = y (t2)  y(t1)
distance travelled = ∫ T
/2 t1 t2 ∫ t1 y ’(t)dt = y(t2)  y(t1) y ’(t)dt +  ∫ t2 T/ 2 y ’(t)dt = y(T/ 2 )  y(t1)  +  y(t2)  y(T/ 2)
The distance travelled (odometer reading or length of path) in the usual (nondistance
mathematical) sense is used to convey the notion “CHANGE in position” But
position”.
in Calculus these two are different. “CHANGE in position” is always with reference
to a coordinate system. If an object moves in a circle o...
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 Fall '09
 TAMERDOğAN
 Limit, Δx

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