We study the capillary rise of wetting liquids in the corners of different geometries and show that the meniscus rises without limit following the universal law: h(t)/a ≈ (γt/ηa)^1/3, where γ and η stand for the surface tension and viscosity of the liquid while $a\,{=}\,\sqrt{\gamma/\rho g}$ is the capillary length, based on the liquid density ρ and gravity g. This law is universal in the sense that it does not depend on the geometry of the corner.

We investigate how drops merging on a nonwettable surface jump off this surface, for both symmetric and asymmetric coalescences. For this purpose, we design and build a microelectromechanical system sensor able to quantify forces down to the micro-Newton scale at a high acquisition rate (200 kHz). Using this device, we perform direct force measurements of self-propelled droplets coupled to high-speed imaging. Experimental data show that the total momentum of the drop after coalescence mainly depends on the size of the smaller drop. Exploiting this finding, we quantitatively predict the takeoff speed of jumping drop pairs and show how to correct the usual argument based on energy conservation.

Data from storms suggest that the critical wind speed at which trees break is constant ($\simeq 42\mathrm{m}/\mathrm{s}$), regardless of tree characteristics. We question the physical origin of this observation both experimentally and theoretically. By combining Hooke's law, Griffith's criterion, and tree allometry, we show that the critical wind speed indeed hardly depends on the height, diameter, and elastic properties of trees.

We study the trajectory of dense projectiles subjected to gravity and drag at large Reynolds number. We show that two types of trajectories can be observed: if the initial velocity is smaller than the terminal velocity of free fall, we observe the classical Galilean parabola: if it is larger, the projectile decelerates with an asymmetric trajectory first drawn by Tartaglia, which ends with a nearly vertical fall, as if a wall impeded the movement. This regime is often observed in sports, fireworks, watering, etc. and we study its main characteristics.

The contraction of a muscle generates a force that decreases when increasing the contraction velocity. This “hyperbolic” force–velocity relationship has been known since the seminal work of A. V. Hill in 1938 [Hill AV (1938) Proc R Soc Lond B Biol Sci 126(843):136–195]. Hill’s heuristic equation is still used, and the sliding-filament theory for the sarcomere [Huxley H, Hanson J (1954) Nature 173(4412):973–976; Huxley AF, Niedergerke R (1954) Nature 173(4412):971–973] suggested how its different parameters can be related to the molecular origin of the force generator [Huxley AF (1957) Prog Biophys Biophys Chem 7:255–318; Deshcherevskiĭ VI (1968) Biofizika 13(5):928–935]. Here, we develop a capillary analog of the sarcomere obeying Hill’s equation and discuss its analogy with muscles. Significance The force generated by a muscle decreases when its contraction velocity increases. This rheology follows the heuristic Hill’s equation. Here, we design and study a capillary analog in which the myosin–actin interaction is replaced by the wetting affinity between a Newtonian silicone oil and a steel rod. This device contracts and generates a force that also decreases with increasing contraction speed, following the same Hill’s equation. The physical origin of this attractive equation is discussed together with the analogy between the actin–myosin system and the capillary one. Apart from its academic interest, this capillary muscle can also have extensions in technology to produce forces and motion using surface chemical energies.

Significance: A volatile liquid placed on a hot plate is known to levitate on a cushion of vapor. Such drops have unusual behaviors, among which is the ability to transform in pulsating stars that sporadically appear for a few seconds. We report that the vapor cushion of Leidenfrost drops spontaneously vibrates, which can trigger the pulsating modes via a Faraday instability. The mediating waves and subsequent peripheric undulations resonate at well-defined drop sizes, which explains their transient nature and the mode hierarchy. These effects illustrate the unique nature of a situation combining hydrodynamics, aerodynamics, and phase change. Beyond the light shed on the origin of Leidenfrost stars, levitating drops also provide toy models for the Faraday instability in open, globular, small-size systems.