Physics Topics are also essential for space exploration, allowing scientists to study phenomena such as gravitational waves and cosmic rays.
What is Motion and Four Basic Types of Motion ? Explain in Detail
A tree is fixed at a place, so we say that it is stationary. Similarly, a house, a school, a factory, electric poles and telephone poles are all stationary objects which remain at a fixed place. On the other hand, a man, animals, birds, car, bus, train, ship and aeroplane, etc., do not remain stationary all the time. T
hey can move from one place to another. For example, a man can walk along a road, an animal like dog keeps on moving here and there and birds fly in the sky. Similarly, a car, bus, train, ship and aeroplane move from one place to another. The movement of an object is called motion. A common characteristic of all the moving bodies is that they change their position with time. We can now define motion as follows :
An object is said to be in motion (or moving) when its position changes with time. For example, when the position of a car changes with time, we say that the car is moving or that the car is in motion. Let us take an example to understand it more clearly.
In Figure we see a car at position A in front of a house and tree at a particular time. After 5 seconds we see the same car at position B which is quite far away from the house.
This means that the position of this car is changing with time. So, we say that this car is moving or that this car is in motion. Some other objects around us which can show different kinds of motion are: bullock cart, swing (jhoola), wind-mill, pendulum of a clock, and the hands of a clock.
If an object moves fairly fast, then its movement (or motion) can be observed easily. But if an object moves very slowly, then it becomes difficult to observe its movement immediately. For example, a wrist watch has three hands: a seconds’ hand, a minutes’ hand and an hours’ hand, which move round and round on the dial of the watch.
Now, the seconds’ hand of a watch moves quickly, so we can observe the move-ment of the seconds’ hand of a watch very easily. But the minutes’ hand and hours’ hand of a watch move quite slow, so their movement cannot be observed easily.
We will have to keep on observing the position of minutes’ hand and hours’ hand for quite some time to find out whether they are moving or not. This is because when an object moves, its position changes with time.
In science, when an object is stationary (not moving), it is said to be at rest. Thus, a house and a tree are stationary (not moving), so a house and a tree are said to be at rest. They are not in motion. Even the same object can be at rest or in motion at different times. For example, when a car is stationary (not moving), it is said to be at rest. But when the car is moving, it is said to be in motion. We will now describe the various types of motion.
Types of Motion
The motion (or movements) of all the objects are not of the same type. Different objects show different types of motion or movements. Some of the important types of motion are :
- Rectilinear motion,
- Circular motion,
- Rotational motion, and
- Periodic motion.
We will now discuss all these types of motion in detail, one by one. Let us discuss rectilinear motion first.
1. Rectilinear Motion
Motion in a straight line is called rectilinear motion. In other words, when an object moves along a straight line path it is called rectilinear motion. For example, when a bullet is fired from a gun, the bullet moves in a straight line path. So, the movement of a bullet fired from a gun is an example of rectilinear motion.
The motion of a cyclist running on a straight road is rectilinear motion (see Figure); the march-past of soldiers in a parade is rectilinear motion; and the motion of a sprinter (short distance runner) running on a straight track is also rectilinear motion.
Some more examples of rectilinear motion are: Motion of a vehicle on a straight road, Motion of a train on a straight track, Motion of a falling stone, Motion of a ball rolling on ground, Motion of a boy sliding down a slope, Motion of a striker on the carrom board, and Movement of the drawer of a table. Rectilinear motion takes place in a fixed direction.
2. Circular Motion
A round path having the shape of a circle is called circular path. When an object moves along a circular path, ills called circular motion. For example, the moon moves around the earth in a circular path (or circular orbit), so the movement of moon around the earth is an example of circular motion (see Figure).
The moon is
a natural satellite of earth. The movement of artificial satellites (man-made satellites) around the earth is also circular motion. The earth moves around the sun in an almost circular path. So, the movement of earth around the sun is also an example of circular motion. In fact, the movement of all the planets around the sun is circular motion.
We can demonstrate circular motion by a simple activity as follows : Take a piece of stone, tie it to a thread and whirl it (move it round and round rapidly) with your hand by holding the other end of thread. We will see that the stone moves along a circular path (see Figure).
Thus, a stone tied to a thread and moved round and round rapidly undergoes circular motion. When the stone tied to a thread is moving round and round, then the distance of stone from our hand remains the same all the time. Thus, in circular motion, the object moves in such a way that its distance from a fixed point (say, the centre of circular path) remains the same.
The movement of tip of the hand of a watch (or clock) on the dial is an example of circular motion [see Figure (a)]. The watch (or clock) does not move from one place to another by itself but the hands of watch (or clock) keep on rotating on its dial.
The tip of any hand of a watch (or clock) keeps on rotating on its dial. The tip of any hand of a watch (or clock) describes a circle on the dial. The distance of the tip of a hand of watch from the centre of the watch remains the same as it moves round and round on the dial.
A ceiling fan (or table fan) remains at one place but its blades rotate round and round. If we mark a point on one of the blades of the fan (with paint, etc.) and switch on the fan, then the point marked on the blade of rotating fan undergoes circular motion [see figure (b)]. In this circular motion, as the fan rotates, the distance of marked point from the centre of the fan remains the same.
The round and round movement of a child sitting on a merry-go-round (or a giant wheel) is also circular motion [see Figure (c)]. Some more examples of circular motion are : An athlete running on a circular track inside a stadium ; A bull tied to a rope and moving around a fixed pole ; and Clothes being spun dry in a washing machine.
3. Periodic Motion
The motion which repeats itself after regular intervals of time, is called periodic motion. The seconds’ hand of a watch takes the same time (60 seconds) to complete each round. That is, the motion of seconds’ hand of a watch is repeated after regular intervals of time (of 60 seconds).
So, the motion of seconds’ hand of a watch is an example of periodic motion. Similarly, the movements of minutes’ hand and hours’ hand of a watch are also periodic motions (which are repeated after intervals of 60 minutes and 12 hours respectively).
The revolution of earth around the sun is a periodic motion because the earth always takes the same amount of time (one year) to complete one round around the sun. The rotation of earth on its axis is a periodic motion because the earth always takes the same time (24 hours) to rotate once on its axis.
The revolution of moon around the earth is also a periodic motion because the moon always takes the same time (about one month) to complete one round around the earth. Some other examples of periodic motion are : Swinging of a pendulum ; Motion of pendulum of a “pendulum clock” ;
Motion of a child on a swing ; Motion of the branch of a tree moving to and fro ; The orbiting of a satellite around the earth ; The vibrations of stretched strings of a sitar (or guitar) when plucked ; and Vibrations of the stretched membrane of a drum (tabla or dholak) when struck. We will now describe why the motion of a pendulum, a swing, stretched strings and stretched membranes are said to be periodic motion.
A pendulum consists of a small metal ball (called bob) suspended by a long thread from a rigid support, such that the bob is free to swing back and forth. A pendulum is shown in Figure (a). Initially, the pendulum bob is at position A.
If we pull the bob of pendulum a little to the left side up to position B and then release it, the pendulum bob starts moving like a swing between positions B and C [see Figure (b)], The swinging of pendulum bob from position B to C, and back to B is called one vibration (or one oscillation).
A pendulum always takes the same time to complete its “one vibration”. Since a pendulum repeats its vibrations regularly after fixed time intervals, therefore, a vibrating pendulum or swinging pendulum is said to have a periodic motion.
A pendulum clock for measuring time is based on the periodic motion of a pendulum. In a pendulum clock, the periodic motion of pendulum is used to drive the seconds’, minutes’ and hours’ hands (see Figure).
Thus, the swinging of pendulum of a pendulum clock is a periodic motion. Please note that pendulum clocks are not much in use these days. Just like a simple pendulum, a swing (jhoola) also undergoes periodic motion (see Figure).
The musical instruments such as sitar (or guitar) have stretched strings or stretched wires which produce sound when plucked (see Figure). When the stretched string (or stretched wire) of a sitar or guitar is plucked, it starts vibrating to and fro and shows periodic motion.
The periodic motion of a stretched string will become more clear from the following activity : Take a rubber band, stretch it and tie it tightly between the two nails as shown in Figure (a).
The position of rest of the stretched rubber band is at point A. Now, let us pluck this stretched rubber band at its centre with a finger. The stretched rubber band will start vibrating back and forth between the positions B and C [see Figure(b)].
Every vibration of the stretched rubber band (when it moves from B to C, and back to B) takes exactly the same time. So, the vibrations of stretched strings (like that of a rubber band, a sitar or guitar) are examples of periodic motion. The vibrations of stretched strings produce musical sounds.
The drums (such as tabla) have thin stretched membranes (or skins) tied over the top of their open ends (see Figure). If we place some tiny pieces of paper on the stretched membrane of a drum (say, tabla) and strike the membrane gently, we will find that the pieces of paper start dancing up and down on the membrane of the drum.
This is because when we strike the stretched membrane of a drum, the membrane starts vibrating (or moving up and down) by a small distance. The tiny pieces of paper move up and down with the vibrating drum membrane and hence appear to be dancing on it.
Thus, when a drum (such as tabla or dholak) is struck, its membrane vibrates and shows periodic motion. The vibrations of stretched membranes (like that of a tabla) also produce musical sounds.
Please note that the periodic motion shown by a pendulum, a swing, stretched strings (of sitar or guitar) and stretched membranes (of tabla or dholak) is actually a special type of periodic motion which is more commonly known as vibratory motion or oscillatory motion.
4. Rotational Motion
When an object turns (or spins) about a fixed axis, it is called rotational motion. For example, a spinning top (lattu) moves round and round on its axis, so the motion of a spinning top is an example of rotational motion (see Figure).
Our earth also turns round and round on its axis like a spinning top. So, the spinning of earth on its axis is an example of rotational motion. Some other examples of rotational motion are :
Turning of the blades of a fan ; Rotation of a wind-mill or phirki; Turning of a potter’s wheel ; Turning of a bicycle wheel; Turning of a ball; Turning of the hands of a watch (or clock) ; and Turning of a merry-go-round (as a whole). Please note that the difference between circular motion and rotational motion is that in circular motion an object as a whole travels along a circular path but in rotational motion, the object spins on its axis.
Objects Having More Than One Type of Motion
Some objects may have more than one type of motion at the same time. In other words, some objects may have a combination of two (or more) different type of motion. This will become clear from the following examples.
(i) The Case of Earth. The earth moves around the sun, so it has circular motion ; the earth repeats its motion around the sun after regular intervals of time (of one year), so it has periodic motion ; and the earth rotates on its axis, so it has also rotational motion. Thus, the earth has three types of motion at the same time : circular motion, periodic motion and rotational motion.
(ii) The Case of Merry-Go-Round. If we consider merry-go-round as a whole, then it shows rotational motion because it turns on an axle. But the outer part of merry-go-round (on which children sit) shows circular motion. So, a merry-go-round has two types of motion at the same time : rotational motion and circular motion.
(iii) The Case of Bicycle. Suppose a bicyle is moving on a straight road. The wheel of bicycle is rotating on its axle and also moving forward in a straight line path. So, a bicycle moving on a straight road has two types of motion : rotational motion as well as rectilinear motion.
(iv) The Case of a Ball. When a ball is moving on the ground, it is rotating as well as moving forward on the ground. So, a ball rolling on the ground has two types of motion : rotational motion as well as rectilinear motion.
(v) The Case of a Sewing Machine. The sewing machine has a wheel which rotates on an axle. So, the wheel of a sewing machine shows rotational motion. The sewing machine has also a needle which moves up and down continuously (as long as the wheel rotates). The needle of sewing machine undergoes a periodic motion. Thus, a sewing machine exhibits two types of motion at the same time : rotational motion as well as periodic motion.