# Physics of Theatre



## damjamkato (May 17, 2011)

So in my physics class we are doing group presentations about the physics of certain things, such as toys, movies, music, etc. My group decided to present about the physics of theatre. We have to teach a 40 minute class, including an activity, about our topic. I already have a lot of ideas about topics to cover, but I'm kind of stuck when it comes to an activity. We will be holding the class in our theater, which is a 3/4 thrust with full light/sound systems, because practical demonstrations of concepts will occur. Does anybody have any ideas for a hands-on group activity, relating to the physics principles behind theatrical technology? Keep in mind that this is a physics class, so nobody really has any experience in terms of theater technology. I need to keep it simple and safe, yet something interesting. Oh, and obviously since rigging is all about physics, we will talk about it, but since we have no fly system, demonstrations are a impossible.


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## LXPlot (May 17, 2011)

Well, a couple ideas come to mind. Y

ou could use a polarization filter to demonstrate how Seachangers work (from my understanding). If your theatre doesn't have any of these I'm sure your physics teacher does. 

You could set up a few lights with the right color gel and demonstrate how Red, Green and Blue can combine for white (color theory). 

You could show mirrors and lenses by opening an old fresnel and showing everyone the reflectors, lense, concentric rings, talking about defraction, etc. 

You could demonstrate resonance with feedback, but this is hard to do on cue and is probably not great for your sound equipment. 

You could take people to where your dimmers are and discuss electrics, circuit breakers, etc. You also could talk about the electrics inside of the fixtures, distros, one phase vs. three phase, etc.

Sounds like a pretty cool project. Wish we had the time to do something like that.


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## natebish (May 17, 2011)

LXPlot said:


> You could demonstrate resonance with feedback, but this is hard to do on cue and is probably not great for your sound equipment.


 
in order to demonstrate that i would ring out the room with the EQ were the class can see it and then talk about resonance and problem frequencies.


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## n1ist (May 17, 2011)

Other than rigging, optics and electricity come to mind as good topics.
/mike


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## Footer (May 17, 2011)

Color, sound waves, electricity, rigging, scenery construction.... theatres are giant physics labs. If you can't find 40 minutes of material I would be amazed.


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## GBtimex (May 17, 2011)

OH what a fun chance you have to explore the world of physics and theatre! 


Here are a few suggestions from things that I have found fun/possible:

Lights:

Light in general is a form of Electromagnetic radiation. So it needs no meduim to travel through. So through some fog in the theatre and explain how you can see the light now because it is going through a medium now (in this case gas)

Color theory: showing how you can create white light with RGB lights. You can also show (with the right equipment) color mixing. This is all about waves 

Optics: show them a Leko inside and explain how a lamp with no Ellipsoidal mirror the light goes everywhere but with it you can increase the amount of light you have by a huge factor. 



Take that same Leko and put a gobo in it and focus it. This shows the nature of lenses and how they work 



Show them a Fresnel and explain how light diverges with this type of instrument and explain the difference.




If you are REALLY passionate about this I would also have a tub of water to shoot through and show interference and how that changes the nature of the light.




Newtonian Physics:


LOADS of fun examples 



A fly system that works on a single or double purchase system can be used for friction, forces at work (and the diagrams that go with that) and elasticity. This can also be used for Vectors. If you have any spare sheaves and blocks you can explain mechanical advantage and how it works. if you can secure this you could lift something REALLY heavy (or a person if you can rig it safely).


If you have J bar you can explain how a Fulcrum works. This also covers the law of Torque but you can do that with a wrench and a bolt just as easily. 



Pendulum: This one is a little scary but it WILL work if done right. Hang a object from a rope. pick up the object and bring it to your face; (allow it to touch your face)then let it go. It will go down, swing up the other way and come back at you. It will STOP about half an inch before touching the person who let it go. You MUST NOT GIVE THE OBJECT ANY FORCE. Simply let it go. It freaks everyone out but it's really cool 







and if you are REALLY crazy (I did this one with my dad when I was a kid) try this one on waves.


Take a pipe (about and inch or 2 wide and about 3 to 5 ft long) secure it to the ground and cap one end with a nipple that can attach to a can of some sort of 

flammable gas. Take the other end and attach it a speaker (Make sure its got a O ring it so it's secure and gas cannot escape). On the pipe drill holes (maybe pencil wide in diameter) and space every 2 to 3 inches down the entire pipe. 



Here is where this gets fun:


Fill the pipe with gas and light the gas. It should look like a row of birthday candles or a menorah. Now if you play ANYTHING through that speaker it will dance and match the wave nature of the sound. If you have an oscilloscope you can make a standing sin wave. The flame will bend and form it. 



We did this once for a physics class in our garage and even though I lost all the hair on my hand and a good part of my arm it was AWESOME. I don't recommend this for just anywhere BUT it will be the remembered. 





I hope this helped some. My father taught physics and was our qusi TD in high school. We loved doing things like this for classes and there is a TON more if you are willing to do some leg work first. If you want more let me know.


Best of luck,


GBTimex


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## shiben (May 17, 2011)

GBtimex said:


> OH what a fun chance you have to explore the world of physics and theatre!
> 
> 
> Here are a few suggestions from things that I have found fun/possible:
> ...


 
The fire one sounds like more of a lab demo for a classroom (thats where we did it at our school). Other than that, the others are pretty good. The one with the swinging ball is great for inertia and pendulums, which are super interesting to begin with. I think lights will probably be your best bet, as color mixing and optics are really easy to demonstrate, quite safe, and are often done poorly in the classroom because the gear that they get is not usually quite as awesome as what we get (well, for RGB mixing). Again, the fire one is cool, but should not be attempted unless you have some qualified people to build and set it up, because its gas and obviously this can be dangerous. Really cool demo if you can make it work.

FWIW, not really a theater demo, but a cool thing you can do is make a vacuum powered ping pong ball cannon with a piece of PVC pipe. Basically all you do is take a pipe, place a ping pong ball in one end, take heavy packing tape, securely fasten it over both ends, evacuate the air down to like 1-2 torr (iirc) and puncture the end of the tube with the ping pong ball at it. The ping pong ball will accelerate to nearly mach, and will shoot through about 3-6 empty pop cans, assuming you did it right.


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## damjamkato (May 17, 2011)

Thanks for all the replies! Actually, we built one of those tubes earlier in the year when we were studying sound. They're called Rubens' tubes, and they're really, really good for visualizing sound wave patterns. (Also, they're lit on fire, so it's cool anyway).


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## ruinexplorer (May 17, 2011)

You also have an opportunity to teach safety if you have the ability to demonstrate shock loads (versus static loads).

In addition, you could look at principles of automation including gear ratios, pulleys, pneumatics and hydraulics. Heck, you can even toss in some theater history with some of these principles and how the ancients used these technologies for their "god machines" and automatons.


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## museav (May 19, 2011)

Footer said:


> Color, sound waves, electricity, rigging, scenery construction.... theatres are giant physics labs. If you can't find 40 minutes of material I would be amazed.


My college physics classes included The Physics of Music and Light, Sound and Optics, those two classes alone were two semesters worth of class material.

And just to clarify, feedback and resonance are two different things and, in fact, resonance or room mode issues cannot be addressed via EQ. If feedback is caused by any room related resonances then you can't vary those resonances by varying the audio signal, all you can do is vary the signal level such that the acoustic loop gain drops back below unity (which is what feedback is).

If you can get two speakers, two signal generators and a delay or two you can show all sorts of resulting acoustical phenomena such as beat frequencies, filling in the fundamental, combfiltering, Haas effect and so on, all of which can be applicable to theatre sound.


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## LXPlot (May 22, 2011)

museav said:


> And just to clarify, feedback and resonance are two different things and, in fact, resonance or room mode issues cannot be addressed via EQ. If feedback is caused by any room related resonances then you can't vary those resonances by varying the audio signal, all you can do is vary the signal level such that the acoustic loop gain drops back below unity (which is what feedback is).



Sorry, I was unclear. I kind of meant a compare/contrast thing in that regard.


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## damjamkato (May 30, 2011)

Thanks for all of the suggestions guys. My group presented on Wednesday, and we got a 100% on the project. Since we only had 40 minutes, we stuck with basic things in light and sound. We ended up covering basic color theory and well as touching on lenses and optics in terms of light. In terms of sound, I talked about how microphones work (and the different types), how speakers work, what causes feedback, and what low impedance balanced XLR does. I also did a demonstration about phase cancellation (speaker, tone generator, two mics equal distances from the speaker, polarity reversed on one of them). Thanks again!


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