This cute, little guy was seen on the back of a sign in the area around Chiang Mai, Thailand. Although the sign was very smooth, this lizard did not slide off. He seemed to have complete freedom of motion in any direction. How can he do this? One answer to this question utilizes knowledge of friction, but there's also a strategy that uses special chemical bonds.

What is "?" in the picture?

We know the force of gravity pulls the lizard downwards, as shown in the picture on the right. So in order for him to stay on the wall, there must be a force of equal magnitude acting in the upward direction. Where does that force come from? The answer depends on what type of creature we're talking about.

What is the mysterious force?

The most common answer is friction. The microscopic interaction between an animals tiny hairs or claws and the climbing surface acts as a force that opposes gravity. However, this strategy requires that the climbing surface have a degree of roughness, like tree bark or bumpy walls. Even walls that look smooth often have enough friction for insects to crawl on them because FG is so small that very little friction is needed to counteract it. For lizards that need friction, smooth surfaces like glass may be unsurmountable. However, there are other mechanisms for "sticking" to surfaces.

How can certain creatures climb on low-friction surfaces?