Displacement

It is a change in the position of an object with respect to time.

Section I :POSITION, DISTANCE & DISPLACEMENT

Straight

Let’s look the picture

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Let’s look the picture

Old position

Let’s look the picture

Old positionNew position

New position

A

B

Can you tell me about rockets A and rockets B!

Old position

Let’s look the picture

Old positionNew position

New position

A

BWe can say, rocket A moving and B No !

Moving object is identified by its change of position from a certain point of reference

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ตำ��แหน่�งอ้�งอ้�งเริ่��มตำน่ สิ้��น่สิ้�ด

•ก�ริ่กริ่ะจั�ด (Displacement) เป"นปร!มาณ vector จัะตำ องม�ขนาด(ระยะที่าง) แลื่ะที่!ศที่าง

•ริ่ะยะท�ง (Distance) เป"นปร!มาณ Scalar ม�เฉพ�ะขน่�ด

Start

Finish

A

B

• Set up a coordinate system –Right is usually positive, left is usually

negative.

– Distance = total length of travel

– Displacement = change in position = final position – initial position or ∆x = xf - xi

• Displacement can be positive, negative, or zero

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• ก�ริ่กริ่ะจั�ดเป'น่เท��ใด• ที่�าอย�างไรจัะที่�าให การกระจั�ดเป"น

ศ&นย'

2 km

4 km

7-11

In this section you are able to :

1. Making a graph of displacement vs time

2. Finding the equation of speed

3. Identifying the application of constant straight motion in daily life

Section II :

• Average Speed and Velocity

Speed is scalar quantity.(Blue curve)

time

cedisv

tan

Unit : m/s

Velocity is vector quantity. (Green line)

time

ntdisplacemev

Unit : m/st

x

tt

xxv

if

if

t

x

tt

xxv

if

if

ix

fx

Base on component that contents of quantities, quantities can be derived in two kind :

1.Vector (velocity) 2.Scalar (speed)

VelocityFor example1.If some one walking 5

km/hour toward east :a. his speed is 5 km/hourb. his velocity is 5 km/hour to east.

Graphical Interpretation of Average Velocity

Slope of a line connecting two points on an displacement vs. time plot is equal to the average velocity during that time interval

The relationship among d, t, and v

t

dv

v

dt

tvd .

d

v t

Calculating the velocityAverage speed is the total

traveled distance divided by the time needed to travel that distance.

t

dv

v = average speedd = total distancet = time total

•We can use the slopeslope of a distance – time graphs to find the speed of an object.

•To do this the graph line must be straight.straight.

t

xSlope

Copy

Slope = velocity

Handout

Calculate the slopeslope for each Car

•The average speed of Car A =•The average speed of Car B =•The average speed of Car C =

Time (h) Speedometer Car A (kmh-1)

0 50

0.5 50

1.0 50

1.5 50

2.0 50

2.5 50

3.0 50

3.5 50

4.0 50

Copy

Identify pleace!

Identify pleace!