Consider a snake climbing up the wall or ant climbing up the wall, which force is responsible for it?
An obvious answer is frictional force but my question is that if there is a normal reaction between the wall and snake, the snake should then be accelerating horizontal direction; which is obviously not the case, which external force is balancing the normal reaction applied by the wall.
If no Normal force between the wall and snake, there is no friction as well.
You might be picturing the whole thing wrong. The walls are not smooth in the real world. Normal reaction has a vertical component, and the weight of the snake is balanced by this.
Let me first say that I am not an expert on snakes, so please do your own research before citing or sharing this answer.
Due to the lack of legs, snakes have to employ a variety of methods to move around. Each of these methods have their own advantages, and snakes choose between them depending on the topography and texture of surfaces they are on. One of those methods is called Lateral undulation, which might be used to climb though rough walls.
In this mode, the snake climbs the wall by hanging on to it, either using its body as a whole or using its scales to cling on surface irregularities on the wall, like a mountaineer climbs using an axe.
This study shows that snakes can actuate their belly scales to actively generate friction for moving forward.
This is an animation I made using Scratch, which might give an idea of how they can move in this position. Check it out!
However, as this study points out, Lateral undulation is one of the slowest mode of locomotion for snakes, and they rarely choose to perform this. If the surface is rough enough or if there is a groove, a snake finds locations where it can latch on to, and pushes its way through (Concertina movement, B).
For climbing poles and trees, they mostly use concertina movements.
In conclusion, for all these methods to work, you need irregularities in the surface, which brings us to the take home message of this discussion. Snakes cannot climb smooth walls. So if you need to keep snakes from climbing into your house, put smooth ceramic tiles/wallpapers on the walls.
References:
The answers vary tremendously by species, but speaking from experience, a sufficiently wet young snake can use the surface tension of the water on their body to pull them to the surface they are climbing.
On a related note, keep a lid on snake enclosures, even if they're flat vertical glass much taller than the snake.
Principally it is due to surface tension (not friction force). Googling something like surface tension insects wall would produce many hit of different level of difficulty (in terms of knowing physics.)
Here is, e.g., the abstract to article Insect-Inspired Wall-Climbing Robots Utilizing Surface Tension Forces:
This paper describes insect-inspired wall-climbing robot that is capable of walking on a smooth vertical surface utilizing surface tension forces. The adhesion mechanism of the robot is inspired from the attachment system of ants, which is responsible for a thin film of secreted liquid between the adhesive organs and the surface. Two kinds of adhesive pads made of PDMS and glass were fabricated using MEMS techniques and adhesive properties were measured. Furthermore, a hexapod robot with the adhesive pads installed on its feet was developed. The robot weighs 9.5g and walks in the alternating tripod gait. It successfully walked on vertical and inverted glass surfaces.
(emphasis is mine)
I used to keep a range of reptiles when I was younger with the goal of becoming a herpetologist. Snakes possess unique scales on their bellies known as scutes, which aid in gripping surfaces like the ground or tree bark to assist in crawling or climbing. One interesting fact about these scutes is that they are made of keratin, the same material found in human fingernails and hair.
The ability of arboreal snakes to climb trees is facilitated by their scales. The scales on their ventral side, or belly, are modified to provide extra grip, allowing them to grasp onto the rough texture of tree bark or vines. Additionally, their scales have small, hook-like structures that further enhance their ability to cling to branches and prevent them from slipping or falling.
From https://vitalfrog.com/snake-climbing-branch-how-snakes-climb-trees-and/
For a more formal, physics-ey discourse, see https://www.pnas.org/doi/10.1073/pnas.0812533106.
