Time Measurements
Time is measured in years, months, days, hours, minutes and seconds but the SI unit for time is the second. All timing devices make use of some regular process. Can you name some regular process? Most clocks use a process which is a regularly repeating motion, such as the swing of a pendulum. Such repeating motions are
termed oscillations. The most accurate clock is the caesium clock (an atomic clock) which depends on the oscillation of a caesium-133 atom. This clock is accurate to a 1 second loss or gain in 6000 years. Since such oscillations are very regular, the time in which one oscillation occurs should be constant. This time is referred to as the period of the oscillation.
The pendulum clock is used to measure long intervals of time. It measures time in hours, minutes and seconds. The gravitational potential energy from the descending mass is used to keep the pendulum swinging. How about clocks and watches? In clocks that are wound up, this energy is stored in coiled springs as elastic potential energy. Watches are also used to measure long intervals of time.
Most modern watches and clocks depend on the vibration of quartz crystals to keep time accurately
The energy to keep these crystals vibrating comes from a small battery. However, there are still many watches making use of coiled springs to supply the needed energy.
Stopwatches are used to measure short intervals of time. There are two types of stopwatches: the digital stopwatch and the analogue stopwatch (which is obsolete). The digital stopwatch is more accurate than the analogue stopwatch as can measure time in intervals of 0.01 seconds while the latter can only measure time in intervals of 0.1 seconds. Before giving the result of the time measurement, it is important to consider other errors involved. For instance, if you use a digital stopwatch to time a race, you should not give the time to
the nearest 0.01 s. Why? The watch may be accurate, but your reaction time in starting and stopping the watch will be more than a few hundredths of a second typically 0.3 s. In some science experiments, you may be required to set up a simple pendulum and to perform some calculations.
1 complete swing or oscillation will be from A to B to C and back to A again.
Period, T is the time taken for 1 complete swing or oscillation. This is measured in seconds or s.
Frequency, f is the number of swings or oscillations in one second. This is measured in Hertz or Hz.
Henceforth, from definitions above, the relationship between T and f will be T = 1/f
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