Distance And Displacement Power Point

Position, distance and displacement

• Position and distance • Position and displacement • Time • Scalar and vector quantities © Manhattan Press (H.K.) Ltd.

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Position and distance Mechanics

Why? study motions of bodies How? 1. position 2. direction 3. time taken 4. other related physical quantities

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Position and distance • position — denotes both the direction & distance from a given reference point • unit of distance: metre (m) / kilometre (km)

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Position of shopping centre X N

1 km east Tracy 1 km

X

1 km north

Shopping centre X from Chris: direction: north distance: 1 km position of Tracy

Shopping centre X from Tracy: direction: east position 1 of km Chris distance:

Chris

1 km

Y 1 km

1 km 4

Position of church Y N

Tracy

X

The position of church Y from Chris:

1 km

direction = south-east distance = 2 km 　　 = 1.41 km

Chris

1 km

Y 1 km

1 km 5

Position of church Y N

Tracy X

The position of church Y from Tracy:

1 km

direction = south-east distance = 8 km 　　 = 2.83 km

Chris

1 km

Y 1 km

1 km 6

The reference point Different reference point

Position changes destination

200 m

starting point

200 m

• Distance from destination = 200 m • Distance from starting point (complete 1 loop) = 400 m 7

Position and displacement • Distance alone is not enough

5m

5m

Distance = 5 m, represents A or B? 8

Position and displacement

How can we solve it Displacement • represents change in position • a physical quantity which has both magnitude & direction

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Position and displacement Displacement of A and B from O: Magnitude =5m direction

Direction:

negative (–)

• Left (−) • Right(+)

5m

−5 m

direction positive (+) 5m

+5 m 10

Position and displacement magnitude of displacement = shortest distance between starting point & end point • independent of the travelled path

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Position and displacement

distance displacement distance

Thinking 1

displacement

length length depend on the travelled path

independent of the travelled path 12

Time Measure the duration of an event Unit: second (s), minute (min), hour (h) a sundial

a stopwatch an atomic clock a quartz clock

a watch 13

Scalar and vector quantities scalar quantity

vector quantity

magnitude only

magnitude & direction

time, distance & temperature

displacement

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