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# Classwork Series and Exercises {Physics- SS1}: Time- Concepts of Time, Ways of Measuring Time, i.e. Both Old and Modern Methods

Topic: Time; Concepts of Time, Ways of Measuring Time, i.e. Both Old and Modern Methods

Both Galileo and Newton and most people up until the 20th century thought that time was the same for everyone everywhere. This is the basis for timelines, where time is a parameter. Our modern conception of time is based on Einstein’s theory of relativity, in which rates of time run differently depending on relative motion, and space and time are merged into space time, where we live on a world line rather than a timeline. Thus time is part of a coordinate. In this view, Physicists believe the entire Universe and therefore time itself began about 13.8 billion years ago in the big bang.

Time itself can be defined as that in which developments and happenings can be distinguishably analyzed with reference to before and after.

In the International System of Units (SI), the unit of time is the seconds (symbol is S). The most natural time unit is the solar day which is manifested by the passing of day and night. It takes the earth one solar day to complete one revolution about it axis. There is also a different time scale known as sidereal used for astronomical purpose. This is the time interval between two successive passages of a star over the meridian. The essential mechanism of the devices used for marking the passage of time are masses, so mounted or suspended that when set in motion under the influence of forces, they repeat with great regularity fixed cycles of their motion. The pendulum of a clock and the balance wheel of a watch are two of such mechanisms.

The Modern Time

Today, we measure and indicate time with clocks. In the laboratory, time is measured with a stop-clock or a stop-watch and both can be started and stopped with the use of a knob which can be pressed and pushed. The stop-watch enables us to accurately measure small intervals of time to 0.1 seconds.

For instance 60 seconds = 1 minutes, 60 miniutes = 1 hour,  24 hours = 1 day.

Pre-historic man, by simple observation of the stars, changes in the seasons. Day and night began to come up with very primitive methods of measuring time. This was necessary for planning nomadic activity, farming, sacred feasts, etc.

The earliest time measurement devices before clocks and watches were the sundial, hourglass and water clock.

The forerunners to the sundial were poles and sticks as well as larger objects such as pyramids and other tall structures. Later, more formal sundial was invented. It is generally a round disk marked with the hours like a clock. It has an upright structure that casts a shadow on the disk – this is how time is measured with the sundial.

The hourglass was also used in ancient times. It was made up of two rounded glass bulbs connected by a narrow neck of glass between them. When the hourglass is turned upside down, a measured amount of sand particles stream through from top to the bottom bulb of the glass. Today’s egg timers are modern versions of the hourglass.

Another ancient time measurer is the water clock or clepsydra. It is an evenly marked container with a spout in which water drips out. As the water drips out of the container, one could note by the water level against the markings what time it was.

One of the earliest clocks was invented by Pope Sylvester II in the 990s. Later on chimes or bells were added as well as dials to the clocks.

Early clocks were powered by falling weights and springs. Later clocks with pendulums came into existence in 1657.

Electric clocks came into being after 1850, but were not popular until the twentieth century. An electric motor with alternating current powers these clocks. Later, digital clocks with LCD (Liquid Crystal Displays) rivaled the electric clocks. Quartz clocks use the vibrations of a quartz crystal to power the clock.

Watches are different from clocks in that they are carried about or worn. The first set of watch appeared in the 1500s and were made by hand. They were very fancy and their faces were covered by fine metal strips to protect the markings. Watches were manufactured by machine in the mid 1800s.

At first, watches had knobs on the outside that the wearer wore to keep the mainspring power inside. Later on, self-winding watches derived power from the movement of the wearer. With the advent of quartz crystal watches with digital displays, the need for motors for watches decreased.

Today’s clocks and watches are increasingly digital devices, often set via satellite guidance, the reason we now have the Greenwich Meridian Time (GMT), Central European Time (CET) etc, such that around the world, countries operate on different time zones, e.g. in USA there are different states with time differences of hours, same applies to continent to continent and country to country.

Tests and Exercises

1. An ancient method of measuring time that made use of shadows formed by the sun was a

A. water clock   B. hourglass  C. sundial. Answer is sundial

2. A device consisting of several glass bulbs connected by a narrow glass neck with grains of sand that flowed from one bulb to the other is a

A. water clock   B. hourglass  C. sundial. Answer is hourglass

3. A container that had liquid pour into it slowly marked at regular intervals that denoted the time was a

A. water clock   B. hourglass   C. sundial. Answer is Water clock