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:- Long ago people did not have any means of transport. They used to walk and carry load on their back or head. They also used animals like horses, bullocks, mules, camels and elephants transport.
Invention of the wheel brought a revolution in modes of transport. Animals were used to pull vehicles such as bullock carts and tongas, that move on wheels.
:- In ancient times, people used hand-span, cubit, arm length and footstep as different units of measurement of length and distance.
· Hand span is the length between the tip of the thumb and the little finger, when stretched.
· Cubit is the length between the tip of the middle finger and the elbow.
· Arm length is the length between the shoulder and the middle finger.
· Footstep is the length between the thumb and the heel of the foot.
The ‘to and fro’ motion or vibrations of an object about it positions of rest is called oscillatory motion.
Example:- The movement of a pendulam and swing is an example of this type of motion.
A very fast to and fro motion is called the vibratory motion.
Example:- The movement of strings in a musical instrument like guitar or the movement of the surface of drums and tabla when played are examples of vibratory motion.
Note:- Other questions are very easy. Do by yourself.
Take a balloon and blow air into it. On blowing air into the balloon, its shape and size changes. Now let the air escape out of the balloon. The balloon gets back to its original shape and size. this is a physical change as balloon can regain its shape and size. Again take a balloon, blow air into it and tie its mouth with a string tightly. Now prick it with a needle. The balloon bursts and cannot get back its original shape and size. This is an irreversible change.
Take some ice cubes and keep them at room temperature for sometime. The solid ice changes to water.
The process of conversion of solid ice into water is called melting of ice.
The process pf conversion of water back into solid ice is called freezing of water. Both melting and freezing are reversible and physical changes.
If you heat the water, it evaporates and changes into water vapour, i.e.., steam.
When steam is cooled, you will get back the water due to condensation.
Both evaporation and condensation are reversible change.
Note:- It will be explained to you in class.
Note:- You already had done it.
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