Types of motion

This theory discuss in the following link my youtube channel 

Introduction:

              Early you learnt that motion is change in position. In order to specify position, we need to use a reference point and a set of axes. 

          Seemingly rest and motion are quite opposite to each other. However, the following example will prove that sometimes it becomes very difficult to say whether a body is at rest or is in a state of motion. 

       For example, imagine that you are travelling by a bus. If you compare your position with respect to the surroundings outside the bus, such as trees, fields, houses, etc., you will find that your position is changing with respect to them. Hence, you are in a state of motion. 

               However, if you compare your position with respect to the surroundings inside the bus, i.e., passengers, walls and roof of the bus, you will find that your position is not changing with respect to the surroundings, and hence, you are at rest.

            If you look around at moving objects, you will notice that they are performing different kinds of motion.

             For example, a car moves straight along the road, an electric fan rotates, and the pendulum of a clock moves sideways in either direction. We shall study the different kinds of motion which an object can have.

Translator motion: 

          

         Fig. A car moving on a straight road

              They move through same distance in the same time; it doesn't matter if you are moving along a straight line or a curved line.

   " The motion in which all the particles of a body move through the same distance in the same time " is called translatory motion.

Examples: 

        

• A car moving along a road. 
• A rolling on the ground. 
• A girl sliding down a slope.
• Pulling out a drawer of a table. 
• Firing of a bullet from a gun. A stone hurled from a catapult.

  The motion of translation is of two kinds :

Rectilinear motion :

 

   Imagine a ball rolling on a smooth floor in a straight line. In such a situation the motion described by the ball is rectilinear motion.

    " When a body moves along a straight line, the motion described by the body is rectilinear motion. "

Examples :

• A train moving on a straight rail track.
• A car moving on a straight road.
• A freely falling stone. 

     A coin moving over a carrom board.   

Curvilinear motion :

      Imagine your car is passing over a curved flyover bridge. In such a situation your car is describing curvilinear motion.

 

    "When a body moves along a curved line, the motion described by the body is called curvilinear motion."

Examples :

 1. A ball thrown upwards at an angle.

 

 2. A car or train moving along a curved road or track.

Circulatory or Rotatory motion :

         Switch on a table fan. What do you notice? The blades of the fan start moving in a circle, about a fixed axis. Such a motion is called the Circulatory motion 

   "A motion in which a body moves about a fixed axis without changing it's position is called the circulatory motion. "

Examples :

1. A spinning wheel or chakra.

2. A spinning top.

3. A potter's wheel.

4. A ceiling fan.

5. The earth revolving around the sun.

Simultaneous motion :

      In some cases, the motion of rotation and motion of traslation occur at the same time.

 

       When a drill cuts through a metal piece, it performs the motion of translation as well as the motion of rotation at the same time.

      Similarly, the ball delivered by a spin bowler describes the motion of translation as well as the motion of rotation.

  Other examples of this kind of motion are wheels of a moving bicycle or a scooter or a car or a train. When an object possesses two or more types of motions at the same time, then that motion is called simultaneous motion.

Oscillatory motion :

    Some objects move as a whole, "to and fro" or "back and forth" along the same path without any change in shape. In such situations the objects are describing oscillatory motion.

 "The to and fro or back and forth motion described by an object as a whole, along the same path, without any change in the shape of the object is called oscillatory motion."

Examples :

1. A boy on a swing.

2. The pendulum of a clock moving to and fro.

3. The pendulum of a sewing machine moving up and down.

4. Similarly, the piston of a motor car, the pressing cylinder of a juice machine at a fruit seller's shop, the piston of a spray pump, etc., all perform oscillatory motion.

Vibratory motion :

     There is another kind of oscillatory motion in which the body does not move as a whole, i.e., the entire object does not move.

  

      All musical instruments, such as guitar, violin, sitar, drums, etc., produce vibratory motion.

        

        Even during breathing, when our chest expands or contracts, the motion is vibratory in nature as all the points on the chest do not move out equally. Thus, vibratory motion can be defined as under:

   "The vibratory motion is a kind of oscillatory motion in which the moving object undergoes change in shape or size."

         

     The above diagram shows a metallic wire stretched between points A and B. When the wire is plucked from the middle, it starts moving up and down. However, the motion is not oscillatory in nature because the whole string does not move up and down. Such a motion is called the vibratory motion. It must be noticed that this motion, a change in shape and size takes place.

Periodic motion :

           If you critically analyse the rotatory motion, oscillatory motion or vibratory motion, you will notice that all objects describing this motion, repeat the motion after a fixed interval of time. Such a motion is described by the objects is called periodic motion.

  "A repetitive motion, which repeats itself after a fixed interval of time is called the periodic motion."

Examples :

1. The piston of a motor car engine running at a constant speed.

2. The swinging pendulum of a wall clock.

3. The needle of a sewing machine running at constant speed.

4. Heart of a normal resting person beats 72 times a minute.

5. The motion of a swing.

6. The movement of the lungs during breathing.

Non-periodic motion :

      There are a number of situations when an object describes a repetitive motion, but not at fixed interval of time. Such a motion is called non-periodic motion.

      

     "A repetitive motion, which repeats itself, but not at fixed intervals of time, is called non-periodic motion."

Examples :

1. A football player running in the field up and down is performing non-periodic motion, as sometimes he runs fast and sometimes slow.

2. When the brakes are applied to a moving vehicle, the motion described by the wheels is non-periodic.

3. A cricket ball rolling down the ground gradually slows down and finally.stops and hence, is performing non-periodic motion.

Random motion :

       An object which suddenly changes it's motion from one kind to another kind is said to have a random motion. 

      For example, take a balloon and fill it with air. Notice the motion of the balloon as the air expels from it. The motion possessed by the balloon is said to be random motion. A flying mosquito, a flying kite and motion of football or hockey player on the ground are some of the examples of random motion. All these objects have no specific path.and they change their motions suddenly, so their motions are said to have a random motion.