|Allen wrench provided by IKEA.|
The Allen wrench shown above, included in my IKEA furniture boxes, is a bit different than a typical Allen wrench. Typically an Allen wrench looks like the following.
Notice that there is a short end and a long end. Either end can be stuck into the screw, but one end is more beneficial than the other. Why? Well, it takes some amount of torque to screw in a screw. Torque = Force * Length of lever. So to apply torque to the screw, you must apply some force to the Allen wrench. If you stick the short end in the screw and push on the long end, the length of your lever is longer and it doesn't take as much force to turn the screw. Put the long end in the screw and push on the short end and you'll find it a much harder task.
You probably already realize that the long end is easier to push from your own life experiences, but there's the physics behind it. So the next time you're using an Allen wrench, take time to explain to your kids how one works.