Thursday, March 18, 2010 11:39 PM

Time, Rate & Speed Notes

♥A. Time

1. Time is the duration of an event which is measured in seconds (s).

2. SI Unit: seconds (s).

3 Other measurements of time include days, hours, milliseconds, and minutes, etc.

4 Instruments commonly used to measure time include mechanical stop-watches, electronic stop-watches and hour-glass.

5 The most accurate method of time keeping is the usage of atomic clocks, where every second is equivalent to a fixed number of periods of radiation from the ground state of the Caesium 133 atom.


B. Rate

1. Rate is the expression of a specific ratio in which measurements of two physical quantities are related to each another.

2. The measurements of the two physical quantities may be of different units, e.g. m/s and m/min, OR km/min and m/min.

Conversation table
Example 1
240m/min = 4m/s

Example 2
12km/min = 12000m/min
= 200m/s

3. Conversation of rates allows us to make a fair comparison when we are using the same rates.

4. Other examples of rates would include cm/s, km/h, $/min, and kg/m2.

C. Speed

1. Speed is the measurement of Distance (m) over Time (s).

2. SI Unit: metre per second (m/s).

3. Other measurement units includes miles/h, yards/min.

4. Speed tells us how fast an object is moving, and it is a rate at which distance is covered over time.

5. As an object may not be of constant speed throughout its motion, there would be a need to calculate its average speed.

6. Average speed is the measurement of total distance travelled over total time taken.