From cockroaches to tanks: The same power-mass-speed relation describes both biological and artificial ground-mobile systems

The physics of the urge to have freedom

Freedom, safety, and ease of movement are innate human urges attributed to conscience along with many other preferences such as attractiveness (beauty), economy, and life. This article addresses the physics basis of the innate urge to have freedom. It unveils the connection between animal freedom and the universal (constructal) tendency toward easier movement and greater access in all evolutionary systems throughout nature (animate & inanimate). The demonstration is made with a model of lack of freedom in animal movement: a man who walks his dog on a leash. When two animals are coerced to move at the same speed, their combined effort (the spent power) is greater than when they move freely, and independently. When the speed of the couple is dictated by the big body (man), the big one walks freely, and the small one must run. Participants in organized movement (life, society) are not equal. All participants move with less effort when they are not coerced to move the same way. The implications of this part of physics (nature) are numerous and help unify the animal realm with the design and evolution of human society. If you want diversity, give the population freedom, not prescriptions.

Animal design advantage from the analogy between friction and body heat loss

When a fluid accelerates as it sweeps a solid surface there are two consequences: the friction and the heat transfer (thermal contact) between fluid and solid increase simultaneously. This is known as the universal analogy between fluid friction and heat transfer. In thermal engineering these two effects are problematic because improved thermal contact is beneficial, and increased friction (i.e., pumping power) is detrimental to overall performance. In the present article we question whether the 'analogy' between these conflicting effects hampers the performance of animal movement. The theory focuses on warm-blooded swimmers and the effects (friction, heat transfer) that result from one change in the configuration of the body. Selected for analysis is a breaststroke swimmer. During gliding while reaching forward the 'one change' is from (a) legs spread apart, to (b) legs held tight together. The theory shows that the change from (a) to (b) has two consequences: greater swimming speed, and reduced body heat loss. In animal design both effects are beneficial, unlike in engineered flow systems. The analogy between fluid friction and heat transfer accelerated the evolution of animal design, and accounts for the 'divergent evolution' of fish and mammals.

Locomotion rhythm makes power and speed

This article addresses two questions, why certain animals (frogs, breaststroke swimmers, hovering fliers, jellyfish) push rapidly against the surrounding fluid and then reach forward slowly, and whether this rhythm of propulsion is a manifestation of the universal phenomenon of design evolution in nature. Emphasis is on the distribution of time periods of locomotion in which, during the driving phase of cyclic movement (the motive stroke, phases 1 and 2, in alternating sequence with the dissipative stroke, phase 3), the work is generated (phase 1) and dissipated (phase 2). The relative lengths of the characteristic times t1 and t2 of the phases 1 and 2, are predicted. The relative duration of the proposed three phases of a cycle is the 'rhythm'. The analysis is based on a model of how the effective cross-sections of the stroking body parts impact the surrounding medium, water, or air, and the total power required to account for the kinetic energy losses during phases 2 and 3, which are due to drag forces posed by the surrounding medium. The body configuration (limbs' cross-sections) determines the limbs' velocities that maximize mean power, and the times t1 and t2 within the motive stroke. Emphasis is placed on the freedom to change the evolving design. Freedom is represented in two ways: the number of degrees of freedom in changing the dimensions of the model and its deformation in time, and the effect that evolutionary changes have on the access that the body has to its available space. Freedom to change the locomotion design leads to greater power and speed.