Why is it harder to open a door handle closer to the lock?


For example, If you grip a door handle normally you can open it with ease. But why is it that it’s so much harder if you move your hand closer to the base of the handle?

In: Physics

A door handle is a lever. The further out on a lever you are, the more leverage you get. Since the lock is usually right on the fulcrum, the closer you get to it the less leverage you have.

moment forces. When you have a lever, the further away you are from the point of rotation (in this case, the base of the handle), the easier it is to move. Think of a wrench. If you try to loosen a bolt with your hand, it’s going to be near impossible to turn. But when you use a wrench, it’s far easier due to the length of the wrench.

Lots of maths and stuff behind it, but that’s the gist of it

Torque is the term that describes the force that is applied when you try to rotate something around a single point. For example, when you open a door, you’re rotating the handle around the base, and in order to successfully open that door, you need to apply a certain amount of torque.

Torque is defined as the distance between the base and the point you’re applying force to multiplied by the force you apply. When your hand is closer to the lock, that distance (we’ll call it r) is decreased. Because r is decreased, the amount of force you apply must be increased by the same relative amount.

I love the door example. You can use it so easily to put rotational mechanics into perspective, torque and moment of inertia to be specific. For example: if you push a door shut close to the hinges, how much more difficult is it to get it to move and how well do you control it once it’s in motion? Conversely, what happens when you close it using the door handle and how well can you control it? Great illustration for those two important aspects that you can’t mathematically “feel”, if that makes sense.

Everyone here has pretty much answered your question, I just wanted to add that. Great question!