Here is a cheap craft project which results in a working model of a lung and diaphragm. The parts are cheap and available in bulk, and the assembly is pretty easy, making this a good project for classrooms. For each toy, you need a plastic wine glass, a 9″ diameter balloon, and a 12″ diameter balloon. All of these cost a few cents apiece and are available at any party supply store.
The wine glass will be overturned, in which case the stem makes a good analogy to the windpipe, and the cup makes a good analogy to the ribcage. A piece of rubber fabric stretched across the opening will mimic the diaphragm, and a smaller balloon threaded through the stem will mimic a lung. The whole assembly looks like this:
The only pre-class preparation that is needed is to remove the tip of the wine glass stem. It is possible to cut the stem with a scissors or shears, but this tends to create numerous cracks and splinters in the brittle polystyrene plastic. You can easily saw off the tip with a hacksaw, but this tends to leave a frayed and jagged surface. In either case, you can easily smooth and melt away any burrs and shards with the brief application of a small flame from a lighter or candle. Be careful, however, because the plastic can catch fire. (The combustion itself is slow and not particularly hazardous, but the fumes of burning plastic can be toxic.)
To assemble the toy, the small balloon needs to be threaded through the “windpipe”, and then folded back over the opening to help hold it in place. Twirling the balloon into a shaft and spinning it through the stem of the glass, i.e. the “neck” of the model, is usually easy enough. Once the lung is in place, the diaphragm needs to be cut out and attached. Either the teacher or the student needs to cut off the top half or two-thirds of the large balloon, producing a puckered disk of rubber fabric, something like a swimming cap. This circle then needs to be stretched over the opening of the cup, i.e. the base of the “ribcage”. You will probably want to have some spare wine glasses on hand, because the plastic is brittle and can easily crack as children try to force the diaphragm into place all the way around the perimeter.
The toy works better if the balloon is partially inflated when the diaphragm is in the “neutral” position. It may help to blow a little air into the lung before attaching the diaphragm, or after assembly, to loosen the diaphragm, allowing air to escape from the cup, blow gently into the “lung” to weakly inflate it, then release the diaphragm resealing the “ribcage”.
Once the toy is assembled, if you pinch the diaphgram and pull out, the lung will inflate; if you press in, it will deflate. If you alternate rapidly (but gently) between pushing and pulling, you may be able to hear the lung huffing, and if you hold the “mouth” near your skin, you may be able to feel the “breath” being exhaled.