Spring fitted doors close by themselves when released. u want to keep the door open for a long time. if you put a half kg stone in front of the open door it does not help.However if you sandwitch a 20g piece of wood in the small gap between the door and the floor , the door stays open. Explain why????
Answers
Answer:
In the First case when a stone is kept, It is unable to keep the door open, this is because the Normal force between the door and block just only equal to the Weight of the Body, which can be easily balanced by the Door.
But in case the Sandwich of 20 g is placed in small gap, it will produce large friction which will only be balanced by the Normal Reaction of the Door. Thus, the Door remains Open for longer time, until and unless the Sandwich is in it.
Also, the above reason can be specified as the,
''It is due to the greater force of friction developed in the second case. The force of friction developed depends upon normal force developed not on the weight of the object.''
''In the first case the normal force developed is only equal to weight of the half kg stone. In the second case the sandwiched piece of wood is pressed down by the door which results in much higher normal force. So the force of friction is much higher too and the small lighter piece of wood is able to stop the door.''
Hope it helps.