Everyday Physics

How Doors Work

Have you ever wondered why it is easier to open or close a door when you apply force on the end opposite to its hinge rather than near the hinge?

This is because of the concept of torque. Torque is the ability of a force to rotate an object. It is this torque which is also responsible for the spinning of a top. The initial spin given by you provides the torque to help keep the top spinning.

Now, when a top is spinning, it rotates in approximately the same time for each rotation. However, different parts of the top are spinning at different speeds. This speed increases as we move away from the centre of the top. This is because, the larger the rotating circle becomes, the more distance is covered for each rotation. Since every rotation takes the same amount of time, the farther we move away from the centre of the top, the faster the point is moving. So for the same rate of rotation and same force applied when spinning, farther points from the centre move faster.

Similarly, in doors, the hinge of the door becomes the centre around which the door rotates(if we look at it from above).

Door.gif

This is why the handle of the door is always found on the end opposite to the hinge.

To summarise,

  • Opening and closing of the door is possible due to Torque, which is the ability of a force to rotate an object.
  • This torque is similar to that responsible for keeping a top spinning.
  • To open or close a door with least effort, apply a force on the end opposite to where the hinge of the door is.

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