Ideas Wanted: World's Simplest Physics Demos

[Farina]

I'm participating in a "Middle School Science Day" event and
need to conduct a series of "World's Simplest Physics Demos."

They need to be contraptions that the kids can build themselves
in about 20 minutes or so.

They need to be limited to very basic physics concepts, i.e.
"mousetrap car" is too engineering-ish. Can you add to the
following list, or suggest better alternatives?

World’s Simplest Motor
World’s Simplest Telescope
World’s Simplest Rocket (Hero’s & Match)
World’s Simplest Steam Engine
World’s Simplest Heat Engine (drinking bird)
World’s Simplest Electric Guitar
World’s Simplest Speaker
World’s Simplest Battery (potato battery)

 

[A.T.]

World’s Simplest Motor

https://www.youtube.com/watch?v=zOdboRYf1hM

 

[Farina]

Yes, thank you. I've been building these for years. My question is whether or not anyone knows of additional activities to add to the list, or better alternatives (as in "is there a better 'world's simplest motor' than the Homopolar Motor"). Thanks anyway.

 

[NascentOxygen]

A soap boat is fun. A paper helicopter. A water-drop microscope.

 

[VCortex]

Pop-pop boats are good, could make a simple pump by wrapping a flexible tube around a pencil to make an archimedes screw.

 

[A.T.]

Pop-pop boats are good

World’s Simplest Steam Engine?

 

[A.T.]

World's Simplest Linear Accelerator

https://www.youtube.com/watch?v=lJW5FG8Egd8

 

[A.T.]

Worlds Simplest Vehicle Transmission

https://www.youtube.com/watch?v=dvyii6QBLtw

 

[Khashishi]

That is certainly a simple motor to build, but the physics behind it is not so simple. I presume the OP wanted something that was both simple in design and in physics.

 

[0xDEADBEEF]

Galilean cannon (worlds simplest cannon)

 

[CWatters]

There are lots of quite simple experiments/demos you could do...

Standing waves on a skipping rope?
Syphons?
Imploding coke cans ?
Interference using water tank?

 

[NascentOxygen]

The strength of soap bubble walls―relating the thinness of the black region to the wavelength of light.

Invisible spying, using the TV remote control in conjunction with a digital camera.

A few dozen plain mirrors each in a brown paper bag, plus an equal number of small buckets of sand. Outdoors, one at a time stand each mirror in the sand and direct the sun onto a timber target. Then uncover all mirrors simultaneously.