Speed and time are terms which are commonly used in our daily life. So, what is Speed? What are its units? Let us spend a few moments to get to know them. He started to move and gained speed. The cheetah saw the prey and started to move rapidly increasing its speed. Here the word speed refers to the rate at which distance is covered by a person, animal or object in a given time. Its just a number indicating the distance covered. It does not include direction per-se when we talk of speed. A parameter that has magnitude, but no direction is called a SCALAR quantity and the one that has speed and direction is a VECTOR. Here speed has magnitude alone with no direction, hence speed is a Scalar quantity.

A fast-moving object like a race car covers a large amount of distance in a short period of time while a turtle covers a very short distance in a comparatively long period of time. Hence the former is supposed to be moving at high speed and the latter is supposed to be moving at slower speed.

The dimension of speed is indicated by the dimension of distance divided by the dimension of time. In essence, you can show it as m/s or km/hr. As a matter of information when you are on sea or are flying, the unit of speed in knots. 1 knot is equal to 1.85 km/hr. The SI unit is m/s or km/hr and the SI unit does not include knots. Light has the fastest speed which is 3 x 10

The Italian physicist is supposed to have first measured speed and arrived at the definition of distance covered in unit time.

When you represent this in the form of an equation it is shown as,

V=d/t, where V is the speed, d is the distance covered and t is the time in which it is covered. The speed at any given instant is called an instantaneous speed. For example, when you are in a car, the speed shown by the speedometer is the speed at that particular instant. Average speed is the total distance covered by the total time taken.

V=d/t, where V is the speed, d is the distance covered and t is the time in which it is covered. The speed at any given instant is called an instantaneous speed. For example, when you are in a car, the speed shown by the speedometer is the speed at that particular instant. Average speed is the total distance covered by the total time taken.

Now to understand the concept of time in brief. It is one of the most difficult concepts to understand. It is one of the most basic concepts, which is not made of up of anything else. For instance, a chemical has, molecule, atoms etc as its basic components. Time, however, has nothing simpler than itself hence it is the most basic concept by itself. You can say time as what the clock reads as we see. According to Sir Isaac Newton, in his classical physics, ABSOLUTE TIME existed independent of the perceiver. It is progressing at a continuous pace, cannot be perceived but can be measured and it can be expressed only in mathematical form. He further went on to state that what we perceive in day to day life is only relative time or apparent time and not absolute time.

Then came Albert Einstein with the concept of relativity and relativistic time. His concept superseded Newtonian concept of time. In relativity, time is part of the universe and is not external or independent of it. Space-time is integral and not independent and that is why an event is always a point in space-time. Something happens at a given place at a given time. Einstein then established the concept of time-dilation proving that time is not the same for every observer and that it is relative. All these went completely counter to the Newtonian concept of time in classical physics.

Now let us try to understand the relation between speed and time and see how it is graphically represented.

Initial speed is represented by the alphabet “u” and final speed is represented by the alphabet “v”. Time is represented as “t”.

If an object is starting from rest, then its initial speed is 0. Imagine a vehicle starting from rest then increasing speed to 15m/s in 10 seconds. It then travels at the same constant speed for another 10 seconds. From the 20

The key thing here is, between the 10

Whenever a body travels at a steady speed, there is no acceleration. In this case between the 10 and 20

Hence in the first 10 seconds, the vehicle goes from 0 to 15 m/s. Here the final speed is 15 and the initial speed is 0 and all this happens in 10 seconds. To calculate the acceleration for this particular section you do 15 – 0 = 15/10 which is 1.5m/s

So it is 0-25 = -25m/s which is the change in speed and this happens in a time of 20 seconds. So the acceleration is -25/20 which is -1.25 m/s

The units can be kms for distance and hours for time and in that case, the speed will be given as km/hr.

In physics, acceleration is referred to an increase in speed and its opposite is called deceleration. Also, there is another aspect of acceleration caused to change in direction. Even if there is no change in speed but if the direction changes there is acceleration. The reason being, velocity is a vector quantity. Any vector quantity has magnitude and direction, so in the case of acceleration, even if the magnitude does not change but if the direction changes there is acceleration. For example: in a circular motion, there is what is called centripetal acceleration. Like speed acceleration also has instantaneous acceleration and average acceleration. Acceleration measured over a very very short interval is instantaneous acceleration.

Acceleration is given by change in speed(m/s) divided by time(s) so acceleration is given in m/s