Motion and Measurement of Distances: science class six
Moving Things Around Us
We see many things around us. Some are moving while some are not moving. Things that are moving are called in motion while things that are not moving are called in rest or static.
Motion and Rest
When a thing changes its position with elapse of time, then it is called in motion. And when a thing does not change its position with elapse of time, then it is called in rest or in the state of rest.
Examples of things in motion:
A running dog, a running car, a cyclist going somewhere, etc. are examples of objects in motion.
Examples of things in the state of rest:
A dog sitting at a place, a tree, an electric pole, etc. are examples of objects in a state of rest.
Types of Movement or Motion
We see many things moving around us. We can observe that the styles of movement of objects are not the same. Some things are moving in a straight line, some are moving on a circular path, and some are moving in a zig-zag way.
Thus on the basis of styles of movement, the motion can be divided into the following types:
(a) Motion along a straight line
(b) Circular Motion
(c) Periodic Motion
(d) Zig-zag Motion
(a) Motion along a straight line: Rectilinear Motion
When an object moves along a straight line, this type of motion is called the Motion along a Straight Line The motion along a straight is known as Rectilinear Motion.
Example:
A dog running on a straight road, a car running on a straight road, a cyclist going along the side of a football ground, etc. are examples of objects running on a straight line and hence are in rectilinear motion.
The motion of soldiers in a march past parade is also an example of Rectilinear Motion.
The motion of sledge pulling by a dog on ice is an example of Rectilinear Motion.
Thus, the motion of anything moving along a straight line is called Rectilinear Motion.
(b) Circular Motion
If an object moves along a circle or a circular path, the movement or motion of the object is called the Circular Motion.
Example
(1) We see the blades of a fan move on a circular path.
Thus, the motion of the blades of a fan is called circular motion.
If we take a point on the blade of a fan, then we find the distance of that point on the blade is always the same while rotating. This means that the movement of that point on the blade is called circular motion.
(2) If a cyclist is going along a circular path, then the motion of the cyclist is called the Circular Motion.
(3) If you move a small piece of a stone tied at one end of a thread by holding another tip of the thread in a circle, then the motion of the stone is called the circular motion.
(4) The movement of the tip of the hand of a clock is in a circular motion.
Thus, anything running or moving on a circular path, then the motion of that object is called Circular Moton.
(c) Periodic Motion
When an object repeats its motion at a fixed interval of time, then the motion is called the Periodic Motion.
Example
The to and fro motion of a swing, the motion of the string of a guitar, the motion of a see-saw, the motion of a pendulum, etc. are examples of periodic motion.
Activity to show the Periodic Motion
* Take a piece of small stone and a long thread (about 20 cm long)
* Tie the piece of stone at one end of the thread
* Hold the other end of the thread in one hand using your toe and fingers and let the stone tied at another end be suspended freely.
* Now pull the stone to one side and free it allows moving freely
You will observe that stone tied with the thread repeats its motion. This is called periodic motion and this type of system is called a pendulum.
In old wall watches there was a pendulum tied at the lower end.
(d) Zig-zag Motion
You will observe the motion of flies and mosquitoes. A fly or a mosquito does not fly in a straight line rather it flies in a zig-zag way. Such motion of a fly or mosquito is called the Zig-zag Motion
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