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14.1 INTRODUCTION  In our daily life we come across various kinds of motions. You have already learnt about some of them, e.g. rectilinear motion and motion of a projectile. Both these motions are non-repetitive. We have also learnt about uniform circular motion and orbital motion of planets in the solar system. In these cases, the motion is repeated after a certain interval of time, that is, it is periodic. In your childhood you must have enjoyed rocking in a cradle or swinging on a swing. Both these motions are repetitive in nature but different from the periodic motion of a planet. Here, the object moves to and fro about a mean position. The pendulum of a wall clock executes a similar motion. There are leaves and branches of a tree oscillating in breeze, boats bobbing at anchor and the surging pistons in the engines of cars. All these objects execute a periodic to and fro motion. Such a motion is termed as oscillatory motion. In this chapter we study this motion. The study of os...

CHAPTER 1 CROP PRODUCTION AND MANAGEMENT Paheli and Boojho went to their uncle's house during the summer vacation. Their uncle is a farmer. One day they saw some tools like khurpi, sickle, shovel, plough, etc., in the field. You have learnt that all living organisms require food. Plants can make their food themselves. Animals including humans cannot make their own food. So, where do animals get their food from? You already know that energy from the food is utilised by organisms for carrying out their various body functions, such as digestion, respiration and excretion. We get our food from plants, or animals, or both. Since we all need food, how can we provide food to a large number of people in our country? Food has to be produced on a large scale. In order to provide food for a large population, regular production, proper management and distribution is necessary. 1.1 Agricultural Practices Till 10,000 B.C.E. people were nomadic. They were wandering in groups from place to place i...