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Physics/Force Entry


QUESTION: I've searched the internet and cannot find physics on doors (Breaking Down). I was wondering if you knew the amount of force it takes to break down a standard wooden door-hollow core.

ANSWER: Where do you apply this force, and how quickly?  Questions this vague (what constitutes a standard door? I'm not in construction.)  Are you kicking it, near the opening part, the hinges, how high, how far apart/how many hinges, what kind of lock and hinges?  Do you want to break it open or kick it completely down?

Don't worry, you just didn't realize that the question was this complex.  Fill me in on specifics, even the frame it's attached to and the screws matter.

---------- FOLLOW-UP ----------

QUESTION: It's technically a make belief door at the moment, but let's say that;

it's hollow core
kicking near the knob
interior door
has regular aluminium lock
and aluminium dead-bolt
has 3 (3-2 style)aluminium hinges
wooden frame of standard width

and the force for breaking it down is

"whatever means necessary" (kicking it in)

the reason I was to know is, not to break into a building but to help improve this strength for under $50.00 (school project)

Then you're asking the wrong question, then, so those specifics won't help you.  It's a relative strength problem to improve the primary failure point of the door, which is where the lock goes into the frame.  That's where the three I've kicked in failed (yes, that does happen to you a couple times in your life).  The absolute force can't be calculated without knowing about that lock, that's what's going to give in during that scenario.  According to this: the shear strength of aluminum should be about 27 MPa, which with a 2cm*2cm bold gives a force equal to (27MPa=F/0.0004m^2) should be a little over a ton of force.  That's not a huge surprise, given the shock forces associated with impacts.  It's a reasonable guesstimate.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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