1. Speed, Displacement and Velocity
Chapter 6
Speed, Displacement and Velocity

2. Time
The SI unit of time is the second (s).
Time is a Scalar Quantity.
In physics, when doing numerical problems, you should always express Time in seconds.

3. Measuring Time In the laboratory we measure time with: a stop-watch,
a stop-clock
or an electronic timer.
Small time intervals are measured in:
minutes (min),
seconds (s),
milliseconds (ms)
or microseconds (μs).
Larger time intervals are often measured in hours, days or years.

4. Different units of time
1 year = days
1 Day = 24 hours
1 hour = 60 minutes
1 minute = 60 seconds
1 ms = 1 millisecond = 1 × 10-3 seconds
1 μs = 1 microsecond = 1 × 10-6 seconds
Question: How many seconds in a year?
Answer:
1 year = (365)(24)(60)(60) seconds = × 107 seconds

5. Distance
The SI unit of distance is the metre (m).
Distance is a Scalar Quantity. Its symbol is s or d.
In physics, when doing numerical problems, you should always express distance in metres.

6. Measuring Distance
In the laboratory we usually use a metre stick to measure large distances.
We use a Vernier Callipers or a Micrometer Screw Gauge to measure smaller distances.
A vernier callipers
A micrometer screw gauge

7. What is Speed?
Speed is the rate of change of distance with respect to time.
Speed is a Scalar Quantity.
The SI unit of speed is the metre per second (m s-1).

8. Speed is the rate of change of distance with respect to time.

9. What is Displacement?
A man walks from A to B, a distance of 68 m, by the path shown.
When he is at B he is 40 metres North East of A.
We say that his displacement from A is now 40 metres North East.
We also say that he underwent a displacement of 40 metres North East in going from A to B.

10. Displacement is distance in a given direction.
Displacement is a Vector Quantity.
The SI unit of displacement is the metre (m).

11. What is Velocity?
Velocity is the rate of change of displacement with respect to time.
Velocity is a Vector Quantity.
The SI unit of velocity is the metre per second (m s-1).

12. What is Constant Velocity?
If an object :
(i) moves in a straight line
and
(ii) does not speed up or slow down
it has Constant Velocity.
The stone is moving in a circle at a steady speed. The direction in which it moves is continually changing. It therefore does not have constant velocity.

13. What is a DistanceTime Graph?
A graph showing how the distance of an object from a given point varies with time is called a Distance  Time Graph.
A Distance  Time Graph for an object moving at a constant speed is a straight line.
The Slope of a Distance  Time Graph is the Speed of the object.

14. Distance – Time Graph Speed of Object =
Find the speed of the object whose distance-time graph is shown.
Speed of Object =

15. A car is on a straight road
A car is on a straight road. Its distance from a pothole on the road is measured. Each of the graphs below represents a different motion of the car. For each one describe the motion of the car.

16. Measuring Constant Velocity with a Ticker Timer and Ticker Tape

17. Measuring Velocity with a Light Gate and a Timer