Recently I was catching up on watching The Big Bang Theory. While the show rarely actual physics aside from the main character, Sheldon Cooper, I did witness something the other day that I thought might be a good topic to research. In the show, one of the characters, Howard Wolowitz's, mother fainted in the bathroom after receiving some bad news, and he had to break down the door, and he had to break down the door to get her to the hospital. His approach: run at the door full speed, shoulder first, and jump into the middle of the door with every ounce of your being - and consequently dislocate your shoulder. There's got to be a better way doesn't there? You see it in the movies all the time. Well, there so happens to be a better way to bust down a door in desperate times. However it should not be done with your shoulder, as that will only result in the same injury (since your shoulder can't handle the force you exert on the door in return), and you must know what your doing beforehand. Upon researching the proper way to bust down a door, here are the steps that I found are the most successful:
1) Assess the door:
Find which way the door swings open. If it is an outward swinging door then you're fresh out of luck with this method - you have a much better chance at breaking your foot. If it is an inward swinging door then try and locate the weak points of the door - the places with the weakest materials (usually near the lock).
2) Get a stable position:
Lean forward and place your foot where you want to kick, and where you are leaning forward at a comfortable angle. This lean will provide you an extra force on the door through gravity.
3) Kick with your heel and hope for the best:
Similarly to Mr. Lefler's post about board breaking, you must imagine yourself breaking through the door and not stop short while kicking. This will allow the maximum Impulse to be applied to the door, as we know J=FΔt. A greater time increases the impulse applied to the door. Make sure to drive your planted heel into the ground during the kick to provide stability and give yourself a better center of gravity. Avoid jump kicks since they take away power (you have no stability on the ground and will lose power).
Remember it's not all about how strong you are, it's about your approach. A well placed kick will do then job every time as long as the door isn't outward swinging or made of metal. While I doubt most of us will ever employ this method, it can't hurt to have another emergency skill under your belt!