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Topic: detect falling object with infra red (urgent) (Read 2243 times) previous topic - next topic

Nick Gammon

You shouldn't need to use analog reads. That will fundamentally slow it down. I did a post here about using an op-amp as a comparator. In fact that was about measuring light:

http://gammon.com.au/forum/?id=11011

Use a simple circuit like that, and then a digital read (and preferably an interrupt). But a loop with a digital read should be OK at those slow speeds.
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Antzy

You should go with interrupts as PaulS suggested. They will give you the fastest response possible. They might seem a bit complicated but will help you out in the long run.


So, 50 mS to drop that distance. Since an ISR can activate in around 3 uS (16000 times as fast as that) you should easily be able to detect even very heavy objects, like elephants, falling.

Sorry to sound like a smart aleck but speed of an object falling has no relation with the weight of object. Galileo showed this by throwing 2 balls of different weights from the Leaning Tower of Pisa :P

technobabologist

That is in a vacuum, wind resistance is a factor for one!

Nick Gammon


Sorry to sound like a smart aleck but speed of an object falling has no relation with the weight of object. Galileo showed this by throwing 2 balls of different weights from the Leaning Tower of Pisa :P


That's OK, I was expecting a comment. :)

I was thinking of Monty Python where they were talking about "what also floats on water?".

"Lead".

"Small rocks".

But you have to admit that foam blocks fall more slowly than elephants. ;)
Please post technical questions on the forum, not by personal message. Thanks!

More info:
http://www.gammon.com.au/electronics

Grumpy_Mike

It's a fair cop.


One of the first things I saw on the internet way back in 1995 was that the most asked question was what does the Witch say in Monty Python, and the second most asked question was what does it mean!

Antzy


That is in a vacuum, wind resistance is a factor for one!

Wind resistance is dependent upon surface area. And surface area has nothing to do with weight. So if u throw 2 balls of same dimensions, but one of steel and one of wood(as Galileo did) from the same height, they reach the ground at same time even though the steel one is obviously a LOT heavier. And this will work even on Earth's atmosphere because the wind resistance will be same on both.

We are getting totally out of the scope of this thread. But i love it :D


But you have to admit that foam blocks fall more slowly than elephants. ;)


Only one way to find out: by throwing a foam elephant and a real elephant from the leaning tower of pisa.  ]:D

dxw00d

Make sure you film that. I want to see it. Although the cell structure of the foam could well influence air resistance.

PaulS

Quote
Make sure you film that.

Especially the part about getting the elephant to the top. Watch where you step.

AWOL

Dave Scott did the experiment on the Moon during the Apollo 15 mission, with a falcon's feather and a hammer (though where they found a spaceflight-certified feather is beyond me)
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

Grumpy_Mike

Quote
Wind resistance is dependent upon surface area. And surface area has nothing to do with weight. So if u throw 2 balls of same dimensions, but one of steel and one of wood(as Galileo did) from the same height,


Yes but Galileo didn't,
Quote
While this story has been retold in popular accounts, there is no account by Galileo himself of such an experiment, and it is generally accepted by historians that it was at most a thought experiment which did not actually take place.

Quote from:-
http://en.wikipedia.org/wiki/Galileo_Galilei#Falling_bodies

Also see:-
http://www.jimloy.com/physics/galileo.htm

PeterH



Wind resistance is dependent upon surface area. And surface area has nothing to do with weight. So if u throw 2 balls of same dimensions, but one of steel and one of wood(as Galileo did) from the same height, they reach the ground at same time even though the steel one is obviously a LOT heavier. And this will work even on Earth's atmosphere because the wind resistance will be same on both.



Sorry for diving off-topic, but the bit in bold above is untrue. The point of the thought experiment is that it only works in a vacuum, because as soon as you introduce atmospheric drag the net acceleration is determined by both weight and aerodynamic drag.
I only provide help via the forum - please do not contact me for private consultancy.

Antzy


Quote
Make sure you film that.

Especially the part about getting the elephant to the top. Watch where you step.

There will be no difficulty taking it up. I'll take a baby elephant and wait for it to grow up.


Yes but Galileo didn't,

Yeah, guess he didnt. But we will! With elephants!


Sorry for diving off-topic, but the bit in bold above is untrue. The point of the thought experiment is that it only works in a vacuum, because as soon as you introduce atmospheric drag the net acceleration is determined by both weight and aerodynamic drag.

Don't apologize. We are ALL totally off topic here. :D

Go through this (Seems like someone already tried out our experiment!):
http://www.physicsclassroom.com/mmedia/newtlaws/efff.cfm
and then this
http://www.physicsclassroom.com/mmedia/newtlaws/efar.cfm

Quote
Subsequently, the amount of air resistance is dependent upon the speed of the falling object and the surface area of the falling object[\quote]
Quoted from the above 2nd link.

Guess you are right that this will not happen on earth. But acceleration is same for both balls(9.8m/s^2). It is not determined by weight or aerodynamic drag(best explanation: www.jimloy.com/physics/galileo.htm and links above). Instead, the heavier ball will accelerate for longer time, hence having more terminal velocity and striking ground first.

technobabologist

Iv just done it and yep elephants do actually fly, amazing!

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