Time: Represents change. The SI unit of time is second (s).
Standard of Time: The second is now defined as 9 192 631 770 times the period of vibration of radiation from the cesium atom.
Instruments used to measure time are: Stopwatches, light gates.
STOPWATCH:
A stopwatch is used to measure the time interval between two events. There are two types of stopwatch.
Mechanical stopwatch and Digital stopwatch.
MECHANICAL /ANALOGUE STOPWATCH:
A mechanical stopwatch can measure a time interval of up to 0.1 seconds.
It has a knob that is used to wind the spring that powers the watch. It can also be used as a start stop and reset button. The watch starts when the knob is pressed once. When pressed a second time, the watch stops While the third press brings the needle back to zero.
DIGITAL STOPWATCH:
A digital stopwatch can measure a time interval up to 0.01 seconds.
It starts to indicate the time lapsed as the start/stop button is pressed. As soon as start/stop button is pressed again, it stops and indicates the time interval recorded by it between start and stop of an event. A reset button restores its initial zero setting.
Smallest measurement Mechanical Stopwatch 0.1 s Digital Stopwatch 0.01 s.
Human Reaction Time: It is the time elapsed between a signal/stimulus is received by humans and the time they take to respond to it.
For most people, human reaction time is about 0.3- 0.5 s.
Light gates: Light gates are used in laboratories to automatically record time to avoid random errors produced in time measurement due to human reaction time.
The Light gate has an infrared transmitter and receiver that will detect a solid object passing through the ‘gate’. Time is recorded as soon as the beam is blocked.
UNIT CONVERSION OF TIME:
