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