Why Are Doorknobs On The Side? Opening The Door to The World of Torque
Open sesame!
A while ago, the Internet has been torn up debating whether there are more doors or wheels. However, why are doorknobs placed on the side, but not the hinge?
This is related to torque, which I will be explaining in this article.
Linear and Angular Equivalents
You may have came across Newton’s Second Law: The net force is directly proportional to mass and acceleration of the object.
The angular equivalent for force is torque. Angular quantities such as angular acceleration or torque only apply to rotational motion, whereas its counterpart applies to linear motion.
Denoted by the Greek letter tau (τ), torque is equal to the product of the distance between the point where force is applied perpendicularly and the magnitude of the force.
The curious reader may wonder how the equation makes physical sense. A freely rotating door is a perfect example of angular rotation.
Force and Torque
Firstly, let’s discuss how force correlates with torque. Grab the doorknob of your nearest door and push it slightly. Then, push the door with a larger magnitude. By pushing the door, you are essentially applying a force on it.
You should realize that the harder you push on the door, the faster it “opens”, or rather rotates. Thus, force is directly proportional with torque.
Distance and Torque
The longer the distance between the force applied and the pivot, the larger the torque. Try pushing the door from the doorknob and you will notice that it would be much easier to open the door than pushing the door from the hinge!
Why must the force be applied perpendicularly to the lever arm?
Open a door and try to push it in a direction parallel to the lever arm. You will notice that the door will not budge.
Thus, torque is only related to the force applied that is perpendicular to the lever arm.
And that’s why doorknobs are placed on the side — to enlarge the torque as much as possible! I hope that this article opened the door to a whole new world of physics for you. Let me know in the comments what you think!
