Slow and Fast Motion

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The motion of an object is defined by its speed, position, direction, and acceleration. Going by the moving objects definition, an object is moving if it changes its position relative to a fixed point. Motion is a relative term and bodies that appear to be at rest could be moving. For example, a book on a table is at rest relative to the table. Still, it moves at approximately 30 kilometers per second relative to the sun (since the earth is revolving around the sun). The speed of the book is even faster when taken relative to the center of gravity. This article will highlight what is meant by slow and fast motion but before that, let us go through few terms and formulas that will help in understanding slow and fast motion.


Examples of Moving Objects

In real life we can find many things moving around us, such as:

  • A ball which is thrown upwards

  • People walking around

  • An airplane flying in the air

  • An autorickshaw moving on the road

  • A ship sailing in the sea

Types of Motion

There are different types of motions that an object can exhibit, and they are discussed below.

  • Rectilinear Motion  

When an object moves in a straight line, it is said to exhibit a rectilinear motion.

  • Periodic Motion

A repeated motion after a fixed interval of time is called a periodic motion. Few examples are the motion of the earth around the sun, a moving pendulum, etc.

  • Circular Motion 

In a circular motion, a body follows a circular path by force applied uniformly along the radius and towards the circle's center.

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Speed of a Moving Object

All objects move at different speeds. Speed is the rate at which an object changes its position in space or covers a certain distance. It is this speed that determines the slow and fast motion of the moving object. An object in fast motion would cover a longer distance compared to an object which is moving slowly with a low speed, in the same amount of time. An object which is not moving at all has zero speed. In old days people would describe speed only as slow or fast. Galileo was the first person to give a formula for speed in terms of the distance covered in a certain duration of time.

The formula for speed is:

Speed = Distance/Time

Speed is a scalar quantity and has magnitude but no direction. Speed can be expressed in several units which are used to measure distance and time. Some of these units are:

  • Miles per hour or mi/h

  • Kilometers per hour or (Km/h)

  • Centimeters per day

  • Light years per century.

Amongst animals, Cheetah has the highest speed for distances under 500 meters and the maximum speed at which it can travel is close to 100 km/hour.


Velocity of a Moving Body

Velocity has a magnitude and direction; hence it is a vector quantity. It is the rate at which a body changes its position. If a person is rapidly walking one step forward and one step back, it might look like a frantic activity, but his velocity is zero. Since the motion results in zero position change  (as the person is coming back to the same position) the rate at which his position changes is zero. When mentioning the velocity of any object, the direction of motion should be stated as well. Hence, if we say that the car is moving at 60 km/hr, it does not completely express its velocity. For example,  60 Km/hr East is a velocity.

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Acceleration of a Moving Body

Acceleration of any object is the change in its velocity per unit time and can be obtained by dividing the object’s change in velocity by time. 

Acceleration = change in velocity/time.

Acceleration applies both to an increase as well as a decrease in speed. The brakes of a car produce retarding acceleration that results in a huge decrease in speed per second. It is termed as deceleration. Acceleration is also a vector quantity, and a change in direction also results in acceleration. The unit of acceleration has two parts; the unit of velocity and of time. For example “10 m/s²”, i.e., 10 meters per second². You can notice that time comes twice in the unit of acceleration, the first is for speed, and the second is for the interval of time in which the velocity is changing.


Types of Speed

  • Uniform Speed 

If an object is covering the same distance in the same time gaps, it is said to have uniform speed.

  • Non-uniform Speed 

If an object covers unequal distances within the same time gaps, it is said to have non-uniform speed.

  • Average Speed 

It is the total distance travelled by a moving body divided by the total time taken in travelling that distance.

Average speed = total distance travelled/total time travelled.

FAQ (Frequently Asked Questions)

Q1. What is Uniform Circular Motion?

Ans: Any object that moves around in a circular path at a constant speed is undergoing a uniform circular motion. An object in uniform circular motion covers the same linear distance every instant of time. The object traverses distance around the perimeter of the circular path. So, if a car is said to have a speed of 6 meters/second in a circular motion, the car is moving 6 meters every second around the perimeter of the path. The distance covered by the object in one complete cycle around the path is equal to the circumference of the circle. The relationship between these three (circle’s circumference, the  time taken to complete one cycle, and speed of the moving object) is an extension of the speed of an object in linear motions and is expressed as:


Average speed = distance/time = 2πr/T, where r is the radius of the circle and 2πr is the formula for the circumference of a circle.

Q2. What is Meant by the Instantaneous Speed of an Object in Motion?

Ans: An object, like a car, does not always move at the same speed at all times. The instantaneous speed of a car can be figured by looking at the speedometer of a car. The speed of a moving object at a given instant of time is called its instantaneous speed.

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