Talk:Trapdoor

"Bert Where's my Sandwich" is a famous quote from the series.

0 google hits; removed pending confirmation. jdb ❋ (talk) 01:27, 5 Mar 2005 (UTC)

A Trapdoor is also called a Stagetrap, which is basically a door in the floor of a stage leading to a secret compartment or dressing room for actor's entrance and exits.

Railway trap doors[edit]

In the USA, trap doors are not exclusive to the so-called "Comet" railcars (a name exclusive to New Jersey Transit; Metro-North Railroad calls their version "Shoreliners" while Amtrak calls theirs "Horizon Fleet" for example). Amfleets, NJ Transit's Multi-Level cars, SEPTA's Silverliners (all generations), NJ Transit's Arrow III EMUs, all of the MBTA commuter rail's fleet (both single- and double-level), MARC's commuter fleet, NICTD South Shore Line cars, Metra's Highliners, and just about all commuter cars of the 20^th Century also have trap doors.

Trap doors are not exclusive to the USA either. Passenger cars operating in other countries on the American continent (Canada and others), trains in France, Germany, Australia, Russia and many other countries feature trap doors also.

71.173.12.59 (talk) 18:40, 25 July 2012 (UTC)[reply]

Acceleration of side away from hinge.[edit]

Note that in motion of a rigid body under gravity, there's nothing stopping parts of it (far from the hinge) accelerating at very high rates - just fix a pointer on it for example. Linuxlad 13:18, 18 April 2007 (UTC)[reply]

You're confusing angular acceleration with linear acceleration. If you raise a rigid body pendulum to a certain height, and release it at the same time as you release a free rest mass from the same height, they will have the same vertical position until they hit the ground, or the pendulum reaches the bottom of its swing. It can't 'accelerate faster than gravity' as there's no other forces acting on it to make it go faster. 128.243.220.22 13:09, 19 April 2007 (UTC)[reply]

Rigid bodies do confuse people. Try the following sequence as clarification:

1) a free lead weight - falls at g

2) weight on an initially horizontal string to a fastener/pivot - bob still falls at g

3) replace string by light strut - bob still falls at g - but linear acceleration of strut is less inboard of bob

4) extend light strut past bob - initial dynamics of bob remain unaffected, but the parts of the strut beyond the bob accelerate at faster than g.

In the case of a gallows door, there are parts of the door that are beyond the CofG and since the door is rigid, they do have forces on them other than their own weight - conversely of course, there is a reaction from the hinge...

The problem of a uniform gallows door is best solved by conservation of energy, so that you don't worry about the reaction at the hinge. I recollect the answer is 1.5g Bob aka Linuxlad 14:02, 19 April 2007 (UTC)[reply]

Yeah, ok. So in my example of dropping a free mass at the same time as swinging a rigid pendulum, the free mass and the centre of mass of the pendulum would remain at the same vertical height. My brain's full of cotton wool today. 128.243.220.42 14:59, 19 April 2007 (UTC)[reply]

But i think maybe it should be phrased "The edge of a trapdoor farthest from the hinge accelerates faster than the victim", rather than "The edge of a trapdoor farthest from the hinge accelerates faster than gravity". Not that it makes a huge difference in the grand scheme of things. 128.243.220.42 15:04, 19 April 2007 (UTC)[reply]