Laser mythology.....

[bschott]

I love how in CSI they use a red laser pointer on a tripod to animate bullet trajectory and their lasers bounce off of every thing, including a yellow painted peice of cement.

And of course in the movie Resident Evil when the blue laser cuts that guy into cubes.

Our local yokles (Fargo Police) have a crime lab team that uses red lasers to animate bullet trajectory. Don't see them around often since we have like 1 shooting every 10 years or so, but a few years back there was a love triangle (wife seperated from husband and started sleeping with a coworker, husband snaps and kills her and her boyfriend, then himself, with a shotgun...very very very shocking thing for this redneck part of the woods) and the local CSI team was there to investigate. I happened to work across the street at the time and watched them set up their lasers. Pretty cool to see red laser beams out of real lasers with no fog. I didn't think laser light was visible unless there was a fog or some particles in the air for the beam to reflect on (I didn't realize higher power lasers will show a beam without fog).

At least there are a few people out there that are trying to educate those of us who are/were part of the "unwashed masses" as it was.

http://www.intuitor.com/moviephysics/mpmain.html#lasers

 

[GooeyGus]

"THAT would be like lasing a stick of DYNAMITE!!!"

Real genius... :worthy:

 

[bschott]

Movies and lasers... always funny isnt it?

I've always found it surprising that holywood moviemakers think that grids of laser beams are commonly used in expensive security systems, but that they are always built such that you can pass between the gaps with enough acrobatics.

As an extra the beams are sometimes invisible (which would make sense), but can be made visible using only some special glasses, no smoke or anything else.

Another holywood thing are sniper rifle scopes that are the size of a ballpoint, yet produce 5 mm wide spots even a mile away.

Someone else was looking at that 'insultingly stupid movie science' page. You pretty much went down the list in the same order to

Nah, nothing bad about that. Good that you pointed it out.

 

[Mr_Lazo]

I, too, used to believe in the wole never-diverging, dot-would-still-be-the-same-size-even-a-mile-away thing. The first time some friends and I were screwing around with lasers at long distances and I saw, first hand, significant beam divergence, I thought my buddy had a cheap laser.

Hollywood lasers are great, though! Anyone remember that scene from Lethal Weapon 4 where (a not yet uncool-crazy) Mel Gibson uses the laser sight on his Beretta to plot the ricochet course of a bullet off of a rusty metal bulkhead and shoots a guy hiding behind some stuff?

 

[Autarchus]

Hollywood lasers are great, though! Anyone remember that scene from Lethal Weapon 4 where (a not yet uncool-crazy) Mel Gibson uses the laser sight on his Beretta to plot the ricochet course of a bullet off of a rusty metal bulkhead and shoots a guy hiding behind some stuff?

I remember that. Good thing that movie came out when I was in elementary school, because after high school physics, movies became (to me) full-retard stupid. A bullet impact isn't elastic, so it would not follow the path of the beam. And any SF soldier will tell you that bullets follow walls.

 

[Deadly]

What does that mean-bullets follow walls?

 

[Morgan]

Soon after getting into this hobby I went to the school my Dad works at, (as a workshop tech. He used to teach but the tech. position is a lot less hassle!), to pick him up. As they have a small CO2 cutting table I was having a look and one of the teachers, (head of year, as it happens), piped up with, "Lasers work better in high wind.". I'm pretty certain wind velocity has very little to do with efficiency! I think he got this idea from the US 747 that was converted to knock down ICBMs.

I didn't have the heart to dispell this myth in front of his class. I might have pointed out that the cutting table should have a high pressure blower to improve cutting!

M

 

[icecruncher]

You can't tell me no one posted "lightsaber" from Star Wars yet. I'm amazed.

There is grade A material!

A self terminating light weapon aka "LASER", with phenomenal power that collapses into a pocket device and can deflect incoming objects. Available in Red, Blue or Green.

Hollywood at its finest!

At least in "Real Genius" the laser continues through objects.

 

[Morgan]

Hmmm.....

Don't know how I missed that one.... lol. What about the Death Star and it's miracle beam combiners?

M

 

[sbdwag]

Though I am 54 years old I always thought until recently that lasers over 5mw were illegal in the USA? I thought they were similar to a class three weapon and It was a federal offence to possess one without a license. I showed a 50mw greeny to some friends at work and they thought they were illegal also.

Regards
sbdwag

 

[LSRFAQ]

public demonstrations of lasers require a variance, basic rule is over 5 mW, you need a projector with a accession number and a variance. If you go over to the CDRH website at FDA.GOV and search for "demonstration lasers"

Steve

 

[game-genie]

I saw that movie where these special forces were rescuring a plane with terrorists and a bomb on it. One of the guys had a Laser with him and he melted the isolation of a cable with it ^^
I know thats the opposite of the topic , because my dilda is able to do that , but I think its also worth to mention some true hollywood myths :-]

game-genie

 

[sbdwag]

public demonstrations of lasers require a variance, basic rule is over 5 mW, you need a projector with a accession number and a variance. If you go over to the CDRH website at FDA.GOV and search for "demonstration lasers"

Steve

I searched the FDA site. And all I could find was regulations concerning manufactures of demonstration lasers and Companys putting on Laser light shows.

Im not sure that showing my laser to two of my close friends at work qualifys as a public laser show demonstration


Regards
sbdwag

 

[lasersbee]

You can own a >5mW laser pointer but you can not Sell a >5mW laser pointer to
or in the USA if the FDA laser safety regulations are not applied.... IIRC

Jerry

 

[Benm]

I saw that movie where these special forces were rescuring a plane with terrorists and a bomb on it. One of the guys had a Laser with him and he melted the isolation of a cable with it ^^

That's a funny new category: laser uses that were mythical at the time the movie was made, but have now come true. Perhaps we can find some old movies where someone started a campfire (or something like that) using a laser pointer.

 

[Autarchus]

What does that mean-bullets follow walls?

When an impact is totally elastic, the projectile will bounce off the impact surface at an angle equal to its incidence. So say the ideal AK-47 bullet hits the ideal concrete wall at 2100 fps and at an angle 45 degrees off the normal - it will ricochet at an angle 45 degrees off the normal and 45 degrees off the plane of the wall, going the same speed of 2100 fps, because in an elastic collision kinetic energy is CONSERVED.

But since bullets are made mostly of soft lead, the impact is very INELASTIC. KE is not conserved. The plastic deformation at the impact and fragmentation of the wall will absorb the energy of the bullet and convert it to sound, heat, breaking molecular bonds, etc..... Thus the angle of deflection will be much LESS than the angle of incidence. The perfect ricochet that is travelling at 2100 fps 45 degrees off the plane of the wall is now going 1300 fps but only 10 degrees off the plane of the wall. Shallower angles of incidence will follow the wall even more closely.

So now when you read Blackhawk Down you'll know exactly why the Delta soldier told the rangers to get out in the street and not to hunker down next to the wall

Light reflections are always of the same angle out as in. So Mel's 9mm bullet would have been far off target after even the first bounce.