Humanoid giants (4 m tall) would be incapable of moving, since doubling the length and width in a proportional manner increases volume and therefore weight by several times, so if such huge creatures exist, either they cannot resemble humans or they are not able to move. This is how the author addresses issues like shape, area and volume as well as their relation to weight. His amusing approach would have made physics a lot more fun at school. He also explains practical matters like "how many books can a standard shelf support without bending and what if you double the lenght..."



The author explains supporting structures like skeletons, towers, pillars, etc. and their stability if they rely on 1, 2, 3, 4 or more legs as well as their mobility (motion on ground, motion in water and flight).



Probably the main differece between nature design and human engineering is a matter of scale, since the majority of living beings are a lot smaller than humans (the scale is shown in an extremely interesting graph). The author mentions that the main difference when choosing a flying method between an airplane and a bird is size and therefore weight, since weight multiplies faster than area. This is why an airplane requires a lot more flight speed. This section is extremely interesting, I will probably read it again.



Other chapters deal with pumps, valves, motors, engines and propulsion systems. I must say that reading through this section was quite difficult, some notions in mechanics are probably helpful. In the end I could manage to understand them after a second reading of some paragraphs (at least the basic concepts or underlying principles, though not the mechanics of the engines itself). This was the only thing that made the book a bit less enjoyable to me.



Finally, the author explains the materials preferred by nature and by the human engineer, as well as their properties (metals as opposed to compound materials like wood, bone, cartilage, etc.). He explains flexibility, rigidity, strength, etc. he basically explains how all this materials react differently to tension, pressure, weight, heat, etc. Metals for example tend to create more heat by friction than natural materials, so cooling systems are an essential part of human made engines.