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BY:

Cahidin Prasetio

09339294

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Learning Objectives

At the endofthis chapteryouare expected to beable to:

1. Define motion.

2. Mention the types ofmotion.

3. Explain the meaningofpath, speed, velocity, andacceleration.

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Motion in Physics is relative, meaning it

depends on the reference point we used. Anobject is consideredmoving when its position

toa reference point always changes.

Define of Motion

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Distance and Displacement

Distance is the total length of travel irrespective of

the direction of motion. It is a scalar quantity.

Displacementis distance moved in the particular

direction. Displacement is a vector quantity.

Suppose that anant moves infigure. Initially it stays

at B, thenmoves straight to A. Lateron it turns to O

and stops.Determine (a) the distance, and (b) the

displacement of the ant.

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Answer

(a).Distance is the total length of travel irrespectiveof the direction of motion. Hence, the distancetaken by the ant from B to A the to O is thelength of BA added by the length ofAO,

d= BA + AO = 5 cm +2 cm = 7 cm

(b).Displacement only depends on the initial and finalposition. Thus, in this case, we only need theinitial position position, which is Xb = +3 cm, andthe final position, which is X0 = 0 cm. The

displacement is XB-A-O = X0 Xb = 0 cm 3 cm = -3 cm.

Thus, the displacement of the ant is 3 cm to theleft.

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Speed and Velocity

Average Speed andAverage Velocity

Average speed is the r atio between distance and

the time interval needed to get the distance..

where:

v: average speed (m/s)

d: total distance travelled (m)

t :total time taken (s)

t

dV !

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Speed and Velocity

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Average VelocityAverage velocity is definedas the ratio between

displacement and the total time taken

Where:

v:Average Velocity (m/s)

s: displacement (m)

t : total time taken (s)

t

X

tt

XXVaverage

(

(!

!

12

12

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Example

An object move straight to the right and takes a distance of 50

m in 12 s. Then it turns to the opposite direction and travels a

distance of 10 m on the same path in 3 s.

What i s (a) the average speed (b) the average velocity?

Answer

(a). The total distance tr avelled is 50 m +10 m = 60 m, and the

total time taken is 12 s + 3 s = 15 s.

Thus, its average speed is (60 m)/(15 s) = 4 m/s.

(b). To calculate its average velocity, first we calculate itsdisplacement;

x = x2 - x1 = (+50 m) + (-10 m) = + 40 m

thus, v = x / t = (+40 m)/(15 s) = +2,7 m/s.

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Next week

1. Acceleration

2. LinierMotion with Constant velocity

3. Liniermotion with constant acceleration

4. Circularmotion

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