雨の日に靴の先端が濡れる理由

When walking outside on rainy days shoe tips, and insteps sometimes get wet. Why do they get wet, despite no contact with road surface. We focus on droplets formed from water film underneath shoe soles. To clarify the shoe wetting mechanism, we captured the motion of the foot and water droplets using a high-speed camera. The movie shows that during walking, droplets were formed beneath the sole, were released from the shoe tip and fell on the instep of the shoe. In the swinging phase, the formation of the primary droplets started when the shoe decelerated and were released in the tangential direction from the shoe sole when the shoe decelerated futher. The secondary droplets were released in the tangential direction of the shoe tip following to the primary droplets. In the rotating phase, the tertiary droplets were formed when the shoe velocity was minimum and released vertically when the shoe started acceleration. After that they accelerated due to the gravity and then fell on the instep of the shoe. Therefore, we concluded that the shoe becomes wet due to the droplets formed when the velocity of the shoe tip accelerated. In the swinging phase, the formation of the primary droplets started when the shoe decelerated and were released in the tangential direction from the shoe sole when futher decelerating. The secondary droplets were released in tangential direction of the shoe tip following the primary droplets.