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We use to open number of doors in daily life. Have you noticed why we always open or close the door by holding it from its open end and not any place near the hinge? If we try to open the door by pushing it near the hinge point then we have to apply a huge amount of force. The door is opened by application of torque and not force.
Take a PVC pipe around 4 ft long. Cut two pieces of approximately 9 inch in length. Now you have three pieces of lengths 9 inch, 9 inch, and 30 inch. Make it in the shape of T with the help of a T joint. This is your danda, apparatus. Ask your friend to hold this danda by keeping the smaller portion in his hand so that the longer portion of the danda is facing you. Instruct your friend to keep the danda in horizontal position. Hold 500 gram of weight very close to the T joint. Now, slide the weight away from the T joint and instruct your friend strictly that he should maintain the horizontal position of the danda. You will notice that as the weight is going away from the T joint your friend find it difficult to hold it in horizontal position. Do this experiment with different people and observe who is holding the weight upto what distance.
The T shape danda can rotate about an axis of the portion of the pipe you are holding in your hand. This axis is known as axis of rotation. When the weight is very close to T shape joint, person feels pleasant to hold it, but as the weight slides away from the joint, person find it difficult to hold. This means, the weight is same but as the distance of weight is increased from the axis of rotation, the torque of the force is also increased. To maintain the T shape danda in horizontal position, we need to apply force in the opposite direction which creates a torque opposite to the torque by the applied weight. As the torque of weight increase, we need to apply more force.
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