It is very common experience that we see the motion of some objects is slow while that of some others is fast.
The distance moved by objects in a given interval of time can help us to decide which one is faster or slower. The distance covered by you after 5 minutes would be much smaller than that covered by any object.
The most convenient way to find out which of the two or more objects is moving faster is to compare the distances moved by them in a unit time. Thus, if we know the distance covered by two buses in one hour, we can tell which one is faster. We call the distance covered by an object in a unit time as the speed of the object.
The speed calculated here is actually the average speed of the object. Here we shall use the term speed for average speed. So, for us the speed is the total distance covered divided by the total time taken. Thus,
Speed = Total distance covered/Total time taken
If the speed is the total distance covered divided by the total time taken. If the speed of an object moving along a straight line keeps changing, its motion is said to be non-uniform. On the other hand, an object moving along a straight line with a constant speed is said to be in uniform motion.
We often need to measure intervals of time which are much shorter than a day. Clocks or watches are perhaps the most common time measuring devices.
One of the most well-known periodic motions is that of a simple pendulum. In the pendulum there has a metallic ball is called the bob of the pendulum.
The to and fro motion of a simple pendulum is an example of a periodic or an oscillatory motion.
The time taken by the pendulum to complete one oscillation is called its time period.
Nowadays most clocks or watches have an electric circuit with one or more cells. These clocks are called quartz clocks. The time measured by quartz clocks is much more accurate than that by the clocks available earlier.
Units of time and speed
The basic unit of time is a second. Its symbol is S. Larger units of time are minutes (min) and hours (h).
To know the speed of an object, we can find the distance moved and time taken by the object. All it's have to do multiply the speed by time. Thus,
Distance covered = Speed x Time
Present information in various forms of graphs. A bar graph is another type of graphical representation.