When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.

When a kinife is sharpened with the help of a rotation grinding stone, the speerk always travel tangentiall to it .Why ?

Radha is a student of class IX in a school in Ambala city in Haryana. Radha's father, Mr. Vijat Kumar, is the Deputy Commissioner of Police in Ambala zone. Radha's family including her father, mother and five year old brother Pulkit, were invited for the celebrations of Air Force Day at the Ambala Air Force Base. During these celebrations, the final item was a fly-past by the fighter jet planes of Indian Air Force. Suddenly there was a loud, explosive noise in the sky over the celebration venue. All the eyes turned up towards the sky. Everybody saw the Indian Air Force's fighter jet planes flying at tremendous speed in a special formation. All the people started clapping for this beautiful and daring fly-past by Indian Air Force pilots. The thunderous sound produced by the speeding fighter planes was so loud that all the birds sitting on the nearby trees flew away. Radha's brother Pulkit was already undergoing treatment for some ear ailment. So, Pulkit got too much pain in his ears due to this intolerable explossive sound. Pulkit was carrying two sharpened pencils with him at that time. He tried to put these pencils inside his ears to get relief from severe pain in the ears. Radha snatched the pencils from Pulkit and warned him not to do it again. Radha was carrying some cotton ear buds in her purse. So, she put cotton ear buds into the ears planes thoroughly. Everyone was praising Indian Air Force for putting up a great show. Jai Ho! (a) What term is used for the extremely loud burst of sound produced by extremely fast, low flying fighter jet planes? What can you say about the speed of fighter jet planes which produce loud bursts of sound (or explosive noise) when the fly? What special name is given to this speed? (c) A fighter jet is flying low at a speed of 1100 km/h. State whether it will produce extremely loud burst of sound or not. Give reason for your answer. (d) Why did Radha prevent Pulkit from putting sharpened pencils into his ears? (e) Why did Radha put cotton ear buds into Pulkit's ears? (f) Name one object which travels at a speed greater than that of fighter jet plane producing loud burst of sound. (g) What values are displayed by Radha in this episode?

When a burning stick of incense is moved fast in a circle, a circle of red light is seen. Give reason

One day, I saw the tree was being cut. I rushed to the site and begged the tree cutters to spare the trunk as it was the home of many a parrot. But I was laughed at and the tree fell with a great thud. I ran to the top end to see two just hatched chicks thrown out of their nest and smashed to death. I looked into all the nests and saw smashed eggs in two of them and one little chick in the other one. Fortunately, the little one survived the fall. I brought it home. The chick can be identified as a parrot only by the shape and colour of its beak. No feathers had come out. I carefully fed it with milk and within two weeks it began to eat bananas, and two months later, it started to fly and I let him fly away. But he would not fly long. He used to linger on the coconut trees in our compound and when I reached home from school, he would fly down and land on my head ! I would show him my finger and he would jump on to it from my head and drink the milk I offered him in a little plate. By putting the sharp end of the upper beak stationary in the plate, he would drink the milk by moving his tongue and lower beak to and fro. Then he would fly on to my shoulder and eat paddy from my palm. Rewrite the following sentences in the ways instructed : I rushed to the site. (Rewrite the sentence using 'used to'.) (ii) The tree was being cut. (Rewrite it beginning with 'They...'.) (iii) I looked into all the nests and saw smashed eggs in two of them. (Rewrite the sentence using the word 'when')

One day, I saw the tree was being cut. I rushed to the site and begged the tree cutters to spare the trunk as it was the home of many a parrot. But I was laughed at and the tree fell with a great thud. I ran to the top end to see two just hatched chicks thrown out of their nest and smashed to death. I looked into all the nests and saw smashed eggs in two of them and one little chick in the other one. Fortunately, the little one survived the fall. I brought it home. The chick can be identified as a parrot only by the shape and colour of its beak. No feathers had come out. I carefully fed it with milk and within two weeks it began to eat bananas, and two months later, it started to fly and I let him fly away. But he would not fly long. He used to linger on the coconut trees in our compound and when I reached home from school, he would fly down and land on my head ! I would show him my finger and he would jump on to it from my head and drink the milk I offered him in a little plate. By putting the sharp end of the upper beak stationary in the plate, he would drink the milk by moving his tongue and lower beak to and fro. Then he would fly on to my shoulder and eat paddy from my palm. What was the parrot's daily routine at the author's home?

One day, I saw the tree was being cut. I rushed to the site and begged the tree cutters to spare the trunk as it was the home of many a parrot. But I was laughed at and the tree fell with a great thud. I ran to the top end to see two just hatched chicks thrown out of their nest and smashed to death. I looked into all the nests and saw smashed eggs in two of them and one little chick in the other one. Fortunately, the little one survived the fall. I brought it home. The chick can be identified as a parrot only by the shape and colour of its beak. No feathers had come out. I carefully fed it with milk and within two weeks it began to eat bananas, and two months later, it started to fly and I let him fly away. But he would not fly long. He used to linger on the coconut trees in our compound and when I reached home from school, he would fly down and land on my head ! I would show him my finger and he would jump on to it from my head and drink the milk I offered him in a little plate. By putting the sharp end of the upper beak stationary in the plate, he would drink the milk by moving his tongue and lower beak to and fro. Then he would fly on to my shoulder and eat paddy from my palm. Do you think, we have deprived the birds of their natural habitats ? What are its effects ?

One day, I saw the tree was being cut. I rushed to the site and begged the tree cutters to spare the trunk as it was the home of many a parrot. But I was laughed at and the tree fell with a great thud. I ran to the top end to see two just hatched chicks thrown out of their nest and smashed to death. I looked into all the nests and saw smashed eggs in two of them and one little chick in the other one. Fortunately, the little one survived the fall. I brought it home. The chick can be identified as a parrot only by the shape and colour of its beak. No feathers had come out. I carefully fed it with milk and within two weeks it began to eat bananas, and two months later, it started to fly and I let him fly away. But he would not fly long. He used to linger on the coconut trees in our compound and when I reached home from school, he would fly down and land on my head ! I would show him my finger and he would jump on to it from my head and drink the milk I offered him in a little plate. By putting the sharp end of the upper beak stationary in the plate, he would drink the milk by moving his tongue and lower beak to and fro. Then he would fly on to my shoulder and eat paddy from my palm. Find out the words from the extract which mean : (i) neatly (ii) stay for longer

When a burning stick of incense is moved fast in a circle, a circle of rod light is seen. Why does this happen? Explain.