Figure 1. Ratchets and droplets.
(a), (b) and (c) show photographs of Blocks 1, 2 and 3 respectively. Droplets travel from right to left. (d) A droplet climbing Block 2. The arrow indicates the direction of motion. (e) A droplet in a flat bowl. (f) Maximum incline the droplets were able to climb for the three blocks. The axis on the right hand side shows the corresponding gravitational force in the backwards direction. TC marks the temperature at which the temperature dependence suddenly changes as described in the body text.