Key Points

In ancient times, people measured time using repeating natural events and devices like sundials, water clocks, hourglasses, and candle clocks.

A simple pendulum consists of a small metallic ball, called a bob, suspended from a rigid support by a thread. It exhibits periodic oscillatory motion.

The time taken by a pendulum to complete one full oscillation is called its time period. An oscillation is one complete to-and-fro swing of the bob.

The time period of a simple pendulum depends on its length but is independent of the mass of the bob. A pendulum of a given length has a constant time period.

The standard international (SI) unit of time is the second, with the symbol s. Larger units are minute (min) and hour (h), where $60 \text{ s} = 1 \text{ min}$ and $60 \text{ min} = 1 \text{ h}$.

Speed is the measure of how fast an object is moving. It is defined as the distance covered by an object in a unit of time.

Speed is calculated by dividing the total distance covered by the total time taken. The formula is $\text{Speed} = \frac{\text{Total distance covered}}{\text{Total time taken}}$.

The SI unit of speed is metre per second (m/s). Another common unit is kilometre per hour (km/h).

The relationship can be rearranged to find distance or time. Distance is calculated as $\text{Distance} = \text{Speed} \times \text{Time}$, and time is calculated as $\text{Time} = \frac{\text{Distance}}{\text{Speed}}$.

When an object's speed changes during its journey, the calculated speed represents the average speed. It is the total distance covered divided by the total time taken.

An object is in uniform linear motion if it moves along a straight line with a constant speed. It covers equal distances in equal intervals of time.

An object is in non-uniform linear motion if it moves along a straight line but its speed keeps changing. It covers unequal distances in equal intervals of time.

Vehicles are equipped with a speedometer to measure and display speed in km/h and an odometer to measure the total distance travelled in kilometres.