- University Physics with Modern Physics. Bauer, Wolfgang & Westfall, Gary. McGraw Hill, 2011
- http://www.harcourtschool.com/activity/science_up_close/305/deploy/interface.html
- http://www.ehow.com/how-does_4651923_door-knob-work.html
- http://www.remodelguide.com/hyhw/shell/142lock.html
- http://www.hometips.com/repair-fix/door-knob-locks.html
Door Knobs