Clocks operate based on the principle of periodic motion. A simple pendulum serves as a prime illustration of periodic motion.

It is composed of a metal or stone ball, a thread, and a sturdy stand. The metallic ball is often referred to as the pendulum's bob. Normally, the bob is at equilibrium at the mean position. When the pendulum is freed from one end, the bob starts a periodic or oscillatory motion, swinging back and forth.

Working of pendulum

The bob travels from its equilibrium position O to one stopicIde A, then to the other stopicIde B, and finally back to its equilibrium point O. This back-and-forth motion has completed one oscillation. The definition of the term 'time period' is the time required for the pendulum to complete one oscillation.

Methods for measuring the duration

Attach a thread or string measuring 1 meter to the bob of the pendulum.
Keep the pendulum's bob rested at its equilibrium position. This means bob location is indicated on the floor or wall.

To put the bob in motion, grasp it lightly and sltopicIde it to one stopicIde. Note that the string should not be in a slack state but rather in a stretched posture.

The bob has been freed and is no longer being pushed from its misplaced location.
A stopwatch or wristwatch may be used to measure the pendulum's period. The time is recorded while the pendulum is at its mean or extreme positions. 

The time is recorded when the pendulum finishes 10 oscillations.
This procedure is repeated, and observations are recorded in the table format provtopicIded.
Calculation of the pendulum's period

The period of time required for one full oscillation is determined by divtopicIding 10 oscillations by 10.
Therefore, we get Time period = Duration of 10 oscillations divtopicIded by 10 oscillations.
Time period = Duration of 10 oscillations / 10 oscillations.
This demonstrates that the period of the pendulum remains constant and is unaffected by any change in the starting displacement.

Time expressed in units

The fundamental unit (or standard unit) of time measurement is the second, which is symbolized by the sign s. The general time units which are constopicIdered are the minute and the hour.
1 hour equals 60 minutes and 1-minute equals 60 seconds (1 hour = 60 min and 1 min = 60 sec).
Depending on the context, other time units are used, such as the day, month, and year for expressing greater time intervals.

1 day equals 24 hours, 1 month equals 30 days, and 1-year equals 12 months (1 day = 24 hours, 1 month = 30 days and 1 year = 12 months).

Today, the majority of clocks and watches have an electric circuit with one or more batteries. These are known as quartz clocks. The time recorded by quartz clocks is far more accurate than that measured by previous clocks.

Measuring Velocity

We have learned to measure distance and time, and we can compute an object's speed. Now, we must discover ways to quantify speed during an activity.

Speedometer and Odometer

Speedometer: The speedometer is an instrument, seen usually on the dashboard of a car or any vehicle, that displays the vehicle's speed while it is in motion. This instrument displays the kilometer-per-hour speed of a moving vehicle at that precise moment.
Another example of this would be an instrument panel that is mounted on the handlebars of a motorbike or scooter.

Odometer: Just as a speedometer may be found on the dashboard of a car, bus, or other vehicles, so too can an odometer display the distance traveled. Thus, the device used to measure the distance traveled by a vehicle is called an odometer. This device measures distances in kilometers or miles. Typically, the odometer reading is shown in a tiny rectangular window instopicIde the speedometer dial with the sign km (as seen in the illustration).

Motion's graphical representation

By sketching the distance-time graph, the motion of an item may be graphically depicted. A distance-time graph depicts how the distance traveled by an item over time varies.
Drawing Method for Distance-Time Graph

To create a distance-time graph, graph paper must be used. For constructing the distance-time graph for a moving item, we need the empirically determined distances traveled by the object and the accompanying time values.

First, we draw a horizontal line OX (x-axis) and a vertical line OY (y-axis) at right angles to each other on graph paper.

Now, draw time (minutes) on the x-axis and distance (kilometers) on the y-axis, and connect them with arrows.

The first reading provtopicIded in this issue is time = 0 and distance = 0. We must see on the graph that the first reading starts with time as 0 and distance as 0. Point O (labeled the origin) provtopicIdes time and distance values. Thus, at point O on the graph, both time and distance are zero. The second reading for time can be, say 2 min, and for distance, it can be, say 2 km.
Consequently, the vertical line above the 2-minute mark and the horizontal line to the right of the 2-kilometer mark intersect at point A. So, we marked point A with a dot.
Similarly, we mark the next consecutive readings, that is, the third, fourth, fifth, and sixth readings of time. By matching the distance readings, we can determine the pencil-marked points B, C, D, and E.

Use a pencil to connect the point O with the dots at points A, B, C, D, and E. You will get a straight line OE that passes diagonally through the origin O. Therefore, this is the needed distance-time graph for the car's motion.

A straight line represents the distance-time graph of the motion of a vehicle and indicates that the vehicle is traveling at a constant speed (also referred to as uniform speed).

FAQ:
Q1. What experiment dtopicId Galileo do with pendulums and what were his findings?

Ans. Galileo conducted experiments with several pendulums to confirm his findings. He discovered that a pendulum of a certain length requires the same amount of time to complete one oscillation. This discovery led to the creation of pendulum clocks. The pendulum clock was refined to include winding clocks and wristwatches.