UNIT 1 Physics on the go

Topic 1 Mechanics

Lesson 1Lesson 1Lesson 1Lesson 1

Describing and recording Describing and recording motionmotion

• Describing motion

• Recording motion

Outline

• Brief introduction of 100 meters race

1.1 Describing motion

• How fast is something moving?

• How far it moved?

Speed

Distance

• How long it took? Time

1.1 Describing motion

1.1 Describing motion

Distance and displacement

• Only 1.5 miles by ferry

• 12 miles by road

How far?

1.1 Describing motion

Distance and displacement

• Distance is defined as the length of path you have taken

• Displacement is defined as the straight line distance

The unit is meters per second (ms-1)

1.1 Describing motion

Speed

1.1 Describing motion

Base SI unit

All the rest are derived units !

1.1 Describing motion

average speed

instantaneous speed

1.1 Describing motion

1.1 Describing motion

Velocity

The unit is meters per second (ms-1)

Speed=? Velocity=?Speed=? Velocity=?

16 meters12 meters

20 meters

Total time= 4 secondsTotal time= 4 seconds

1.1 Describing motion

Acceleration is how quickly velocity changes over time. 

Speed

0

2

13 meters/second

1.1 Describing motion

Acceleration

1.1 Describing motion

Acceleration

• What’s the unit for acceleration?

The acceleration is calculated using:

tu-v

atime (s)

acceleration

(ms-2)

initial velocity (ms-

1)

final velocity (ms-1)

1.1 Describing motion

Acceleration

meter per second per second ( ms-2)!

1.2 Recording motion

Traditional method

• Stopwatch

• Ruler

1.2 Recording motion

( Information and communications technology )

ICT method

• Light gates

• Timer

1.2 Recording motion

ICT method

( Information and communications technology )

Gatso speed camera

Why we need electronic sensors?

1.2 Recording motion

• Will not suffer from human errors

• Reaction time

• Misreading of scales

• Could replay the image to ensure the position