Although organisms obey the same physical laws as inanimate objects the evolutionary implications of these laws are often neglected. Physical factors influence the fitness value of traits and play an important role in the course of evolution. These are the areas of investigation that interest us.
Leidenfrost drops – liquid drops that levitate on a layer of their own vapor over a hot surface – have been all the rage in recent years. We’ve seen how they can be guided, trapped, and self-propelled. What you see here is a bit different. This is a droplet of room-temperature ethanol deposited on a bath of liquid nitrogen. What levitates the droplet in this case is vaporous nitrogen evaporating from the bath.
The droplet is quickly cooling down; it freezes after its second or third bounce off the side walls of the beaker. What causes the droplet to self-propel is an asymmetry of the thin vapor layer beneath the droplet. As soon as some instability causes a slight difference in the thickness of the vapor layer, that triggers the propulsion, which the drop maintains even after freezing. (Image and research credit: A. Gauthier et al.)