How is Time Measured?
Time measurement is not an easy procedure. It isn't very easy for many. So, how is time measured, you will first need to work on how is a minute, an hour or a day measured. In ancient times, people noted the fact that certain periodic happenings never changed. These included the changes in seasons and the sunset and sunrise. These were probably the very first attempts that our ancestors made towards measuring time. The whole procedure was quite simple and the results gained were pretty accurate. The sundial was the very first device used for measuring time. For the ones who do not know what is the study and science of time measurement called, the answer is horology.
How is Time Measured Using Periodic Motion?
Periodic motion is the movement of a particular object that tends to repeat itself after a specific time. The time taken by the object for repeating its movement is called the period, which is measured in seconds. The number of movement repetitions taking place every second is called frequency. The unit used for measuring frequency is hertz. Periodic motion or happenings such as sunrise and sunset were formerly used for measuring time. Other periodic movements used for time measurement include the phases of the moon; the changing of the seasons; the water flow and the movements of the stars in the sky.
Here, it is essential to note that the moon takes approximately 29.5 days to change its phase from one full moon to the next phase. Hence, this periodic movement was the most natural way of measuring a month in ancient times. The changes in seasons marked the beginning and the end of a year. Take, for example, monsoon takes exactly a year to return, and thus our ancestors kept track of the number of days in a year by keeping a watch on the changes in seasons. Measuring a year was quite crucial, considering that human beings depended on the rains for their crops. Proper knowledge about the rains was essential for raising a good yield. With advancements made in the field of technology, more sophisticated ways of measuring time came to the forefront. Later, simple pendulums started being used for measuring time. As long as the bob weight and pendulum length remained unchanged, the pendulum oscillates at a constant pace.
5 Ancient Time Measuring Devices
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This image depicts various types of time measuring devices.
There can be no doubt in the fact that time has played an essential role in the existence of human beings on this planet. We live in the times of clocks and watches using the quartz technology for time measurement. But, in ancient times, time was measured using different ways. There were different time measuring devices used in ancient times. Initially, the natural phenomena around were used for the measurement of time in ancient times. The very first instruments used for time measurement were the mountain and the stick. As shadows shortened, it would be noon, and as they lengthened, it would be night. The five most popular ancient time measuring devices are:
Obelisks or Sundials
Sundials were widely used in 1500 B.C for dividing the interval of time between sunrise and sunset in 12 different parts. Obelisks of ancient Egypt made during 3500 B.C were the oldest shadow clocks used for measuring time. Shadows moving to various marks helped the Egyptians in calculating time, and thus they divided a day into two sections.
Sand-Glass
Hour-glasses or sand-glasses made of a couple of conical glasses linked vertically through a narrow neck were used for measuring time in the 14th century. The sand-glass was for measuring the passage of a period. The width and size of the glass along with the sand quantity in both the sections denoted it. Use of a sand-glass was a more accurate way of measuring time than a candle clock or water clock.
Candle Clock or Water Clocks
These instruments were for measuring time by observing the flow of water from a container or into a container. In the candle clock, the candle was marked using numbers, and the melting wax denoted the period. The time calculations varied with the use of these instruments mainly because of variations in the flow of water.
Pendulum
Galileo Galilei came up with the process of using a pendulum for measuring time. The movement of the pendulum was ideal for keeping track of the period. Way back in 1930, the pendulum was considered one of the most accurate instruments for measuring time. It was Christian Huygens who invented the pendulum clock in 1658 and later the motion of the pendulum started being used as a way of measuring time.
Quartz
The Quartz clocks came into being in the 1930s with Albert Eisenstein proposing the theories of relativity and defining time as the fourth dimension.
In these present times, the piezoelectric crystal, known as quartz, is used for measuring time. Instruments used to measure time in physics include lasers and atomic inventions. In the future, other modern forms of time measuring devices will be appearing in the market for sure.
FAQs on Time Measurement
1. What is the fundamental principle used for the measurement of time?
The fundamental principle for time measurement relies on using a phenomenon that repeats itself regularly. This is known as periodic motion. Any event or motion that occurs at consistent intervals can be used as a time-keeping standard. Historically, these included the rotation of the Earth (day and night), the phases of the moon (month), and the revolution of the Earth around the sun (year). Modern devices use the consistent oscillations of a pendulum or a quartz crystal.
2. What is the SI unit of time, and how are other common units related to it?
The SI (International System of Units) unit of time is the second (s). Larger, more common units of time are defined based on the second. The key relationships are:
- 1 minute (min) = 60 seconds (s)
- 1 hour (hr) = 60 minutes = 3600 seconds
- 1 day = 24 hours = 86,400 seconds
3. What were some of the earliest devices used to measure time before mechanical clocks?
Before the invention of modern mechanical clocks, ancient civilizations developed several ingenious devices to measure time. The most notable ones include:
- Sundials: These used the changing length and position of a shadow cast by a gnomon to track the time of day.
- Water Clocks (Clepsydra): These measured time by the regulated flow of water into or out of a vessel.
- Sandglasses (Hourglasses): These used the flow of fine sand from an upper bulb to a lower one to measure a fixed duration of time.
- Candle Clocks: These were candles with markings at regular intervals; as the wax melted, the passage of time was indicated.
4. How did the simple pendulum improve the accuracy of time measurement?
The simple pendulum revolutionized timekeeping due to its property of isochronism, first observed by Galileo Galilei. This means that for small oscillations, the time taken for a pendulum to complete one full swing (its period) is constant, regardless of the swing's amplitude. This predictable and regular motion provided a much more reliable and accurate 'beat' for regulating the mechanics of a clock than the inconsistent flow of water or sand, leading to the development of the pendulum clock by Christiaan Huygens.
5. What is the difference between periodic and non-periodic motion in the context of timekeeping?
Periodic motion is a motion that repeats itself at regular, equal intervals of time. Examples include the swinging of a pendulum, the vibration of a quartz crystal, or the Earth's orbit around the sun. This regularity is why periodic motion is essential for timekeeping. In contrast, non-periodic motion does not repeat itself at regular intervals. Examples include a car moving down a street or a ball rolling to a stop. Such motions are unpredictable and cannot be used as a basis for a clock.
6. Why is a Caesium atomic clock considered the most accurate standard for time measurement?
A Caesium atomic clock is considered the most accurate standard because it is based on a fundamental, universal, and unvarying property of nature: the vibrations within a caesium-133 atom. The second is officially defined based on the time it takes for this atom to undergo 9,192,631,770 transitions (vibrations). Unlike a mechanical pendulum, which can be affected by temperature or gravity, these atomic vibrations are incredibly stable. This results in an accuracy so high that an atomic clock would lose or gain only about one second in millions of years.
7. How does the piezoelectric effect make quartz clocks work?
Quartz clocks work because of the piezoelectric effect in a tiny, fork-shaped quartz crystal. When an electric voltage from a battery is applied to the crystal, it begins to vibrate at a very precise and stable frequency (typically 32,768 times per second). An electronic circuit counts these vibrations and uses them to generate regular electric pulses, one per second. These pulses then drive the motor that moves the clock's hands, ensuring highly accurate timekeeping.
8. Beyond daily use, why is the precise measurement of time critical in the field of physics?
In physics, the precise measurement of time is critical because it is a fundamental quantity in many core concepts and formulas. It is essential for:
- Kinematics: Calculating velocity (distance/time) and acceleration (change in velocity/time).
- Dynamics: Measuring force, momentum, and energy, which often depend on time.
- Wave Phenomena: Defining frequency (cycles per unit time) and period.
- Relativity: In Einstein's theory of relativity, time is treated as the fourth dimension and is shown to be relative, affected by gravity and velocity.
