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PHYSICS OF PLACING A DOOR HANDLE

 

         Kick a ball on the ground.  It goes in a straight line.  OK.  Here you are applying a force straight on the ball.  Suppose, you turn a car driving wheel, what exactly you are doing?  You hold the wheel at the edge and apply a force perpendicular to the axis of rotation.
     We will take another example to understand more clearly.  The opening and closing of a door is also a rotation.  Here, you push the door horizontally at the edge.  That is, you are applying the force perpendicular to the axis of rotation and at a distance from the hinges(axis of rotation).
     This kind of rotating or turning force is called torque.  It is the product of the force applied and the distance from the axis (Torque = F * r).
From the formula, we can understand, if you either increase force or distance, the torque will also increase.

     Suppose, a mechanic wants to loosen a heavy bolt in a machine.  He takes a spanner or a wrench and applies a force as explained above to create a 'turning effect'.  If he fails, he takes another rod attaches to the instrument and tries again.  He mostly succeeds this time because he has doubled the length of spanner and hence doubled the torque.  This is an easy way to magnify a turning force.
     Coming to our door, if the handle is placed at the edge, it is easy to close and open the door.  If the handle is placed at the middle or near the keel, it is going to be difficult, because the torque will decrease.
     Consider a Bi-cycle.  The shaft connected between the center of gear and the pedal is called crank-shaft.  The crankshaft converts the linear motion of the feet into rotatory motion of the gear and also provides the necessary torque.  The length of the shaft determines the torque.  Crank-shaft also exists in all the vehicle engines.
     Turning effect is based on a lever action. "Give me a place to stand," Archimedes is said to have promised, "and I will move the world."
     The above statement clearly illustrates that a length can multiply a turning force many times.  
              ------------------------------------------------------------- 

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