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Author Topic:   Counter-Intuitive Science
Cat Sci
Member
Posts: 9817
From: near St. Louis
Joined: 01-27-2005
Member Rating: 1.9


Message 76 of 182 (600220)
01-13-2011 12:07 PM
Reply to: Message 66 by Dr Adequate
01-12-2011 9:50 PM


Once I was walking towards a set of sliding doors. I noticed them open and close for a group of people walking ahead of me, but when I came to them they wouldn't open. Judging that the sensors weren't sensitive enough to detect my modest weight, I decided to leap vertically in the air in the hope that when I came down the extra force of my impact would open the doors. It did not, and couldn't have done.

Why not?

Because it employed an optical sensor and not a pressure one.


This message is a reply to:
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Cat Sci
Member
Posts: 9817
From: near St. Louis
Joined: 01-27-2005
Member Rating: 1.9


Message 77 of 182 (600222)
01-13-2011 12:12 PM
Reply to: Message 75 by frako
01-13-2011 11:50 AM


. If the rope is longer so the marine can put the rope at an angle by walking a few feet away from the grandpa he can lift the grandpa if he is strong enough

Not if he's standing on ice... There's gonna be a horizontal component to the force that the friction between his feet and the ground will have to overcome.


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Dr Adequate
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Posts: 13099
Joined: 07-20-2006
Member Rating: 2.1


Message 78 of 182 (600225)
01-13-2011 12:34 PM
Reply to: Message 76 by Cat Sci
01-13-2011 12:07 PM


Because it employed an optical sensor and not a pressure one.

Obviously I'd have been wrong if I'd been wrong about how the door worked. But I'd also have been wrong if I'd been right about how the door worked (which I was).


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slevesque
Member (Idle past 1162 days)
Posts: 1456
Joined: 05-14-2009


Message 79 of 182 (600251)
01-13-2011 3:15 PM
Reply to: Message 66 by Dr Adequate
01-12-2011 9:50 PM


I never do well with these kind of questions:

I think it could have at the moment you jump, since you are pushing on the ground to get yourself a vertical, upward acceleration.

Couldn't when you came down since the only force in play is your weight (and the normal force of the ground)


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dwise1
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Posts: 2223
Joined: 05-02-2006
Member Rating: 3.7


Message 80 of 182 (600255)
01-13-2011 3:30 PM
Reply to: Message 66 by Dr Adequate
01-12-2011 9:50 PM


I believe that motion detectors are much more common nowadays than pressure pads, which I don't think I've even seen since my childhood 40 years ago. Assuming that it requires detecting motion towards it, jumping vertically would not involve any motion towards it and so should not trigger it. As for why it didn't detect your initial approach, I don't know, unless you arrived in some time interval when it's designed to not look, such as when it has opened for someone, at which time a different sensor would keep it from closing until after the last person had entered. Did you approach from a highly oblique angle? Though when I do that to a door, it still detects me. Many even detect me walking past; must be my electro-magnetic personality.
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Iblis
Member (Idle past 418 days)
Posts: 663
Joined: 11-17-2005


Message 81 of 182 (600261)
01-13-2011 4:26 PM
Reply to: Message 78 by Dr Adequate
01-13-2011 12:34 PM


weight vs mass
I'm a little baffled. You seem to be saying that the door did detect pressure on the ground. If so, yeah, you should have been able to knock this over whatever minimum was required by jumping on it.

Calling this pressure "weight" shouldn't make any difference. Standard scales, the spring and lever kind for example, veer up all out of proportion when you jump on them. Some sort of stable mass-register, might not, but, what in the world ... my imagination starts to fail me at this point.

Give.


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ringo
Member
Posts: 10162
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 1.7


Message 82 of 182 (600266)
01-13-2011 5:07 PM
Reply to: Message 77 by Cat Sci
01-13-2011 12:12 PM


Catholic Scientist writes:

There's gonna be a horizontal component to the force that the friction between his feet and the ground will have to overcome.


Yes, it becomes a complex vector problem with no easy intutitve answers.


"I'm Rory Bellows, I tell you! And I got a lot of corroborating evidence... over here... by the throttle!"
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Cat Sci
Member
Posts: 9817
From: near St. Louis
Joined: 01-27-2005
Member Rating: 1.9


Message 83 of 182 (600267)
01-13-2011 5:11 PM
Reply to: Message 82 by ringo
01-13-2011 5:07 PM


Yes, it becomes a complex vector problem with no easy intutitve answers.

Just create a free body diagram in your head


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ringo
Member
Posts: 10162
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 1.7


Message 84 of 182 (600272)
01-13-2011 5:30 PM
Reply to: Message 83 by Cat Sci
01-13-2011 5:11 PM


Catholic Scientist writes:

Just create a free body diagram in your head


Yes, the first step is to recognize that you need to analyze the problem, not just jump to the "obvious" conclusion that the stronger man wins.


"I'm Rory Bellows, I tell you! And I got a lot of corroborating evidence... over here... by the throttle!"
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CosmicChimp
Member
Posts: 305
From: Muenchen Bayern Deutschland
Joined: 06-15-2007


Message 85 of 182 (600274)
01-13-2011 5:42 PM
Reply to: Message 66 by Dr Adequate
01-12-2011 9:50 PM


Could it be that the sensor was aiming at the other side of the sliding doors? Was it that you were using the doors but not in the proper direction; an entrance for an exit or vice versa?
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jar
Member
Posts: 25116
From: Texas!!
Joined: 04-20-2004
Member Rating: 1.3


Message 86 of 182 (600276)
01-13-2011 5:44 PM
Reply to: Message 85 by CosmicChimp
01-13-2011 5:42 PM


Like belly buttons.
Doubt it, that was tried back in Message 67.


Anyone so limited that they can only spell a word one way is severely handicapped!
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Cat Sci
Member
Posts: 9817
From: near St. Louis
Joined: 01-27-2005
Member Rating: 1.9


Message 87 of 182 (600280)
01-13-2011 5:49 PM
Reply to: Message 84 by ringo
01-13-2011 5:30 PM


Yes, the first step is to recognize that you need to analyze the problem, not just jump to the "obvious" conclusion that the stronger man wins.

I thought the "obvious" conclusion was that the heavier man wins...

The marine *could* lift him if he could walk backwards with the rope and pulled at an angle.


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RAZD
Member
Posts: 16227
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


Message 88 of 182 (600286)
01-13-2011 6:28 PM
Reply to: Message 12 by Tanypteryx
01-10-2011 10:58 AM


That there are no green stars even though there is green light in their spectrum.

there is a green blob ... or is it the green goblin?

http://news.sciencemag.org/...confirms-nature-of-myster.html

Enjoy


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

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ringo
Member
Posts: 10162
From: frozen wasteland
Joined: 03-23-2005
Member Rating: 1.7


Message 89 of 182 (600288)
01-13-2011 6:32 PM
Reply to: Message 87 by Cat Sci
01-13-2011 5:49 PM


Catholic Scientist writes:

I thought the "obvious" conclusion was that the heavier man wins...


I've actually done the experiment with a little guy who thought he was stronger than me.


"I'm Rory Bellows, I tell you! And I got a lot of corroborating evidence... over here... by the throttle!"
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RAZD
Member
Posts: 16227
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.3


Message 90 of 182 (600289)
01-13-2011 6:33 PM
Reply to: Message 80 by dwise1
01-13-2011 3:30 PM


tripping stoplight sensors with a bicycle
if you are bicycling and come to a stop light that senses vehicles, you can trip the sensor by laying your bike down over the sensor area (usually visible as a rectangle in the pavement) because they use electrical inductance, which falls off with distance squared ...

Enjoy


we are limited in our ability to understand
by our ability to understand
Rebel American Zen Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

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