Question 1 what are stationary objects. Give examples?
Question 2 What is meant by circular motion? Give example?
Question 3 What is meant by rectilinear motion?
Question 4 What is meant by rotational motion? Give example?
Question 5 What is meant by periodic motion? Give example?
Question 6 When an object is said to be in motion?
Question 7 Give few examples to show that object can have more than one type of Motion?
Question 8 Give a difference between circular motion and rotational motion?
Objects which remain fixed at a place e.g. tree, house, school, factory, telephone pole, electric pole are called stationary objects.
On the other hand, men, women, animals, birds, car, bus, bicycle, train, aeroplane, ship etc. do not remain stationary all the time, they can move from one place to another. The movement of an object is called motion.
A common characteristics of all the moving bodies is that they change their position with time. 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 car is in motion.
If an object is 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 i.e. a second’s hand and minute’s hand and an hour’s 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 movement of the seconds’ hand of a watch very easily. But the minutes hand and hours hand of the watch move quite slow, so their movement can not be observed easily.
When an object is stationary (not moving), it is said to be at rest e.g. house and tree are stationary, 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.
Types of Motion
- Rectilinear motion,
- Circular motion,
- Periodic motion and
- Rotational motion.
Motion in a straight line is called Rectilinear motion, e.g.
(1) 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.
(2) The motion of a cyclist running on a straight road is Rectilinear motion.
(3) The march past of soldiers in a parade is Rectilinear motion and
(4) The motion of a sprinter (short distance runner) running on a straight track is also called Rectilinear motion.
(5) Motion of a vehicle on straight road, motion of a striker on the carrom board, motion of train on a straight track, motion of a falling stone, movement of the drawer of a table, Motion of a boy sliding down a slope .
Rectilinear motion takes place in fixed direction.
When an object moves along a circular path, it is called circular motion.
(1) The moon moves around the earth in a circular path, the movement of moon around the earth is an example of circular motion.
(2) The movement of artificial satellites around the earth is also circular motion.
(3) The movement of earth around the Sun is also an example of circular motion.
(4) Movement of all the planets around the Sun is circular motion.
(5) The movement of tip of the hand of a watch on the dial.
(6) A ceiling fan remains at one place but its blades rotate in circular motion.
(7) The round and round movement of a child sitting on a merry go round (or a giant wheel) is also circular motion.
(8) An athlete running on a circular track inside a stadium.
(9) A bull tied to rope an moving around a fixed pole is also an example of circular motion.
The motion which repeats itself after regular intervals of time, is called periodic motion.
(1) The motion of seconds’ hand of a watch is repeated after regular intervals of time, the motion of seconds’ hand of a watch is an example of periodic motion.
(2) The revolution of earth around the sun is periodic motion because the earth always takes the same amount of time to complete one round around the sun.
(3) The rotation of earth on its axis is a periodic motion because the earth always takes the same time to rotate once on its axis.
(4) The revolution of moon around the earth is also a periodic motion because the moon always takes the same time to complete one round around the earth.
(5) 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.
(6) The orbiting of a satellite around the earth, the vibrations of stretched membrane of a drum ( dholak or tabla) when struck.
A pendulum consists of a small metal ball (also called as bob) suspended by a long thread from a rigid support, such that the bob is free to swing back and forth. Initially the pendulum is at position B. If we pull the bob a 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 A and C. The swinging of pendulum bob from position A to C, and back to A is called one vibration. A pendulum always takes the same time to complete its “one vibration” or oscillation. 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.
The musical instrument such as guitar or a sitar have stretched strings or stretched wires which produce sound when plucked. When the stretched strings (or stretched wires) of a sitar or guitar is plucked, it starts vibrating to and fro and shows periodic motion.
Tabla or drums have thin stretched membranes tied over the top of their open ends. If we place some tiny pieces of paper on the stretched membrane of a drum (Tabla) and strike the membrane of the drum and strike membrane gently, 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 the drum, the membrane starts vibrating by small distance. The tiny piece of paper move up and down with the vibrating drum membrane and hence appear to be dancing on it. Thus, when a drum (dholak or tabla) is struck, its membrane vibrates and shows periodic motion. The periodic motion shown by swing, pendulum, stretched strings and stretched membranes is actually a special type of periodic motion which is more commonly known as vibrating motion or oscillatory motion.
When an object turns (or spins) about a fixed axis, it is called rotational motion.
For example: The motion of a spinning top, the spinning of earth on the axis, turning of the blades of a fan, rotation of a wind mill or phirki, turning of a ball, turning of the hands of watch, turning of potter’s wheel, turning of a bicycle wheel.
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.
Object which can have more than one type of Motion
(1) Example 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 earth also rotates on its axis, so it has rotational motion. Thus, the earth has three types of motion at the same time i.e. circular motion, periodic motion and rotational motion.
(2) Example of Merry Go around – If we consider merry go around as a whole, then it shows a rotational motion because it turns on an axle. But the outer part of merry go round shows circular motion. So, a merry go round has two types of motion at the same time i.e. rotational and circular motion.
(3) Example of bicycle – Suppose a bicycle is moving on a straight road. The wheel of a bicycle is rotating on its axle and also moving forward in a straight line. So, a bicycle moving on a straight road has two types of motion rotational motion as well as rectilinear motion.
(4) Example of sewing machine – The swing 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 log 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 i.e. rotational motion as well as periodic motion.
|Notes for Chapter 10 Motion and Measurement of Distances|