(Image: E.H. Shepard)
In the original Winnie the Pooh stories, Pooh and Christopher Robin like to play a game that they call "Poohsticks." This consists of standing on a bridge and dropping sticks over the upstream side. The person whose stick emerges on the downstream side the first wins.
If you play, it would be a good idea to master the physics of the game in order to optimize your performance. Experts at the Royal Academy of Engineering have figured that out. Ideally, a Poohstick is covered with bark, fairly heavy, and dense. The Daily Telegraph reports:
The main variables that need to be considered are cross sectional area, density, buoyancy, and drag.
Usually large objects are slowed down by drag but in water the large size will allow it to be swept along more quickly by the water.
“When it comes to Poohsticks the tubbier the better,” said Dr Rhys Morgan, Director of Engineering and Education at the Royal Academy of Engineering. “If more water is able to influence the trajectory of the stick, it will accelerate more quickly.
“Generally, a rough stick will create more drag than a smooth stick, so in general, bark is good.”