Before looking at models, here is one more kind of practical work: project work. A project usually means visiting a real place, studying it, and then writing a report with ideas for making it better. For example, a class might visit a nearby temple or cultural site, look at how clean and green the area is, and then write a report suggesting ways to improve it.

Some things simply cannot be looked at directly. Nobody can stand outside the solar system and see all the planets at once. Nobody can watch their own lungs working from inside their chest. An eclipse happens rarely, and when it does, you cannot pause it or turn it around to see it from another angle. In every one of these cases a model solves the problem, by making a small, safe, patient copy of something that is otherwise too big, too hidden, too fast, or too rare to study.

A collage is a model made by collecting small objects or pieces and sticking them onto a surface. Using paper or other things found nearby, a collage can show something like an atom, a food chain, or how plants make their own food. It is the simplest kind of model to build, because it needs almost nothing beyond paper, glue, and a clear idea of what you are trying to show.

A globe is a model of the Earth. Looking at a globe, we can see that the Earth is round and tilted slightly, the way a real globe usually stands. Photos of the sun and planets, or drawings of them, can also be collected and arranged to make a collage of the whole solar system.

A model is only useful once you know which real thing each of its parts is standing in for. Read this table, then look at Figure 1.10 again and point to each part on the picture.

Here is what actually happens when you pull the large balloon down. Pulling it makes the space inside the bottle bigger. The air already inside now has more room, so it spreads out and pushes less hard. Air from outside, which is still pushing at its normal strength, is therefore stronger, and it flows down the tube into the two small balloons, filling them. Let go, the space shrinks again, and the air is pushed back out. Your own breathing works the same way. Your diaphragm pulls down, your chest space grows, and air flows in on its own. You do not suck air in so much as make room for it.

This is the most important idea in the whole topic, and it is one that many students miss. A model is never the real thing. It is always simpler, and the person who built it chose what to leave out. A good scientist knows both what a model shows and what it quietly ignores.