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# Basic Physics lesson-3 : Acceleration

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## Introduction

If we recall we learned about speed and velocity in an earlier lesson Basic Physics lesson-2 : Speed and velocity. Now it is time to go ahead and learn about what acceleration is and what is its significance. We will see step by step in this article as what acceleration is and how it is calculated and what learnings we get by knowing about it.

## What is acceleration?

Earlier in article Basic Physics lesson-2 : Speed and velocity, we learned that velocity is the rate of change of displacement. Velocity may be constant or changing. While changing it could increase or decrease. This is the moment where acceleration comes in picture. If the velocity is increasing we say that the body is accelerating. If the velocity is decreasing we say that body is deaccelerating. When we start our bike or car we increase the throttle or press the accelerator so that its speed picks up and increases to the desired level. During this initial time the acceleration is the crucial element based on which people exclaim that their vehicles are having good pick up.

Anyway, in Physics we define the acceleration as the rate of change of velocity. For example if a body has a velocity of 12 meter per minute and in next 5 minutes time it attains a velocity of 18 meter per minute then the acceleration would be equal to change in velocity divided by the time taken. In this case it would be equal to (18 - 12)/5 = 1.2 meter per minute2. Please note that unit of acceleration is derived from dividing the unit of velocity by the unit of time. That is why we get square of minute in the denominator.

We have taken the velocities in meter per minute just for understanding purposes. Normally we should follow a unit system like M.K.S. where displacement is in meter, mass is in Kilogram and time is in second. In such a system the unit of velocity would be meter per second and accordingly the unit of acceleration would be meter per second2.

## Application

Knowledge of acceleration helps us in many ways to calculate the distance traveled or the final velocity of the body. Some of the fundamental equations of motion in classical Physics are based on this entity.

As an example, let us go through the first one which is very simple to derive. Let us denote initial velocity by u, final velocity by v, time by t, and acceleration by a (in some text books symbol f is used for acceleration in place of a).

By definition, acceleration is rate of change of velocity. It means that in 1 second the velocity would change by an amount equal to a. So we can comfotably write for that 1 second v = u + a. In the same way for 2 seconds we can write v = u + 2a. Extending this logic further we get for time t the famous equation v = u + at.

What is the significance of acceleration? When we have to increase the velocity of a body then we have to decide as how much acceleration we have to create and for creating it appropriate force is to be applied on the body. For example when we launch a rocket to Moon we provide it much acceleration so that it attains a high velocity and escapes out of the Earth's lap and proceeds ahead to moon. Incidentally this velocity is known as escape velocity which is in fact very very high at about 11.2 km/second. That is why so much propulsion force is required in launching a rocket to Moon or Mars.

## Force and Acceleration

When a body is in stationary position then we have to apply a force on it to move it and it will move with a velocity depending on the force and if we continue that force the velocity may increase further and if we also increase the force than it will move faster and faster. During this change of velocity we say that it had acquired an acceleration and we have already seen the examples for that in the preceding paragraphs.

Let us now try to learn as how the force applied on a body is related to the acceleration produced in it. Before that, first we have to understand that what happens when we apply a force on a body. Let us take an example in which we give a push to a ball placed on the ground with our leg, the ball will move ahead and after some time it will stop. Why does the ball stop? The ball stops because we did not continue pushing it and though it moved initially but due to the frictional force between the ground and itself the ball stopped after moving for a distance which of course depends upon the initial momentary force applied. The frictional force works in a reverse direction to the movement of the body and that is the reason why the body eventually stops.

What will happen if there is no friction? It is of course a hypothetical situation in our real life as friction will always be there. Anyway, if friction is not there then the body will move ahead and keep moving. This was the thing that led Sir Issac Newton, the great scientist to mention that - If a body is moving in uniform motion it will remain moving like that only and if it is at rest then it will remain at rest until some net external force is applied on it. This is known as Newton's first law of motion. This is one of the most important law to understand the motion of bodies under the applied forces.

Newton gave us three laws of the motions and the second one deals with the acceleration. Newton’s second law states that the acceleration of a body as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. This is a very important observation and the relationship between force and acceleration is explained by this law very nicely.

Acceleration generated in an object is proportional to the force applied on it and inversely proportional to its mass and by combining these two we get -

a (acceleration) = F (force) / m (mass)

That is the universal equation used in Physics for calculating accelerations of the bodies under certain forces applied on them. The MKS unit of acceleration is meter per second2.

## Conclusion

Acceleration is the rate of increase of the velocity of a body and it is a vector quantity just like velocity as it has got a direction. If we want to increase the velocity of a body then we require some force to do it and that force is responsible to create that acceleration in it. More force one applies, more acceleration is created increasing the velocity manyfold. If force is just sufficient to move it at a constant velocity then there is no acceleration. Understanding the concept of acceleration helps us learning the motion of bodies under applied forces.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on May 07, 2020:

Sharmaji, thanks a lot for sparing your time.

S C Sharma on May 07, 2020:

Topic well explained. Useful for beginners and teachers

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on May 07, 2020:

Dr Vijai, thanks a lot for your encouraging comment.

Dr vijai pratap singh on May 07, 2020:

Very useful, explained quite clearly in simple and systematic words.

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 06, 2020:

Anurag, thanks for your nice comment. Appreciate.

Anurag on March 06, 2020:

Very nicely explained and feel nostalgic to refresh all the basic yet useful concepts of Physics!!!

Keep posting more!!

Umesh Chandra Bhatt (author) from Kharghar, Navi Mumbai, India on March 04, 2020:

Flourish, great to rekindle those memories. Thanks for your visit and comment. Highly appreciate.

FlourishAnyway from USA on March 04, 2020:

This brings back memories of physics class from high school.