Torque Torque is basically a measure of how much a force acting on an object will cause it to rotate. This force is usually measured in foot/pounds. The “object” is usually called a pivot point, and for our purposes, a hinge pin will be that pivot point. A screw, which needs to be turned into or out of a door or frame, is also a pivot point, but let’s focus on the door and hinge first. In Figure 1 I’m pushing a door open with my hand placed about a foot away from the hinges on a 36" door. Will I be able to open the door? Probably, but it won’t be easy and will require a lot of pressure. In Figure 2, I’m pushing the door open where a person would normal- ly push: close to the lock edge of the door, almost three feet away from the hinges. The door will be easy to open. Why? First, a little basic geometry review. Look at Figure 3. You see a circle with a dot at its center. I’ve drawn a line from the center dot to the outer edge of the circle, marked “A.” The distance from the center of a circle to its outer edge is the radius. For our purposes, the center of the circle is a pivot point. The distance from one side of a circle to the other is the diam- eter. So, the radius is half of the diameter. The radius is the most important part of all of this. I want you to imagine a hinge pin as be- ing a pivot point in the center of a circle. The door is attached to the pivot at one end and is 36" wide, so the radius of the circle is also 36". The door is acting on an “object” (the hinge) to make it rotate. Where you put your hand on the door to open it is where you are applying force. Look at Figures 1 and 2 again and try it yourself on a nearby door. When your hand is 12" from the hinge/pivot point, it’s difficult to push the door open; when your hand is 36" away, it’s a lot easier to open the door. When you push the door WWW.ALOA.ORG open, you’re using it to apply torque to the pivot point. The further you move away from the pivot point, the easier it is to apply torque. Another way of looking at it is using a screw as a pivot point. Let’s say you have an Allen bolt to tighten down. You have an L-shaped Allen wrench; The short leg is 1” and the long leg is 4". If you insert the end of the 4" leg into the bolt and try to turn it us- ing the 1" leg, you won’t be able to tighten it much. If you insert the 1" leg and turn with the 4" leg, you’ll apply so much torque that you might actually strip the screw. What’s happening is that when you move away from the hinge and toward the end of the radius and apply the same pressure, you’re increasing the torque ap- plied to the pivot. Notice that it gets easier as you get further away because of that. If you’ve ever seen someone slide a piece of pipe over a wrench, usually referred to as using a “cheater,” to loosen a stuck bolt, it’s the same idea. Increase the radius; get more torque with less effort, increasing your mechanical advantage. Herein lies the problem with this: If it takes less effort, but you use the cheater with all your strength, you’re applying a tremendous amount of torque to the bolt and wrench and either one of them could break under the stress and injure you or the part, and possibly both. Keep this in mind going forward because I’m going to tie this into screws and fasteners later on. What’s also involved with doors and hinges is leverage, but it’s different from torque. Torque is rotational and leverage is generally movement in a straight line. You might hear someone with a cheat- er saying he wants more “leverage.” It’s similar, but not the same. The lever and fulcrum together are one of the of the six Figure 3. A review of geometry helps to explain the concept of torque. In this im- age, the center dot of the circle to its outer edge is the radius. The distance from one side of a circle to the other is the diameter (twice the radius). basic machines that most modern ma- chines are descended from. Another ex- ample is the inclined plane: A screw is a descendent of the plane in that a screw is an inclined plane wrapped around a shaſt. Leverage is somewhat like torque be- cause the further down the lever you get away from the fulcrum, the greater the mechanical advantage. In other words, it will get easier to apply liſting force, and as you apply more force to the lever, you multiply the force exerted against the ob- ject you’re liſting. This is how they were able to build the pyramids with simple machines. How this applies to doors, and to us, is this: You’ll oſten see someone stick a door wedge, broom handle or piece of wood be- tween the door edge and the frame near the hinge to keep the door open. Jani- tors love to do this. What happens is that whatever is used to wedge the door open has now become a fulcrum and the door is a three-foot long lever. Let’s suppose someone leans against the MAY 2016 KEYNOTES 49
