why can you stick different parts of your body(head, hand, finger) in small gaps really easily but you can’t take them back out?
In: Physics
One of the reasons (besides the mentioned swelling) is that when you push, say, an arm through a gap, you are stretching skin and flesh (think pulling up a sock), which makes the limb thinner.
When you are pulling it out, skin and flesh crumples in the gap and makes the limb thicker.
To see it in an easier way: Wear a loose sock in your hand, and push it through a gap (for example between two couch pillows). Its stretches going it, but crumples when pulling out.
My guess is it relates to the skin. When the skin is pulled back and taut, it makes the area less wide, or smaller in a sense.
If you hold your hand out with the palm side down, and push the skin on the back of your hand towards you/back, it smooths down closer to your bones.
If you then push the skin up towards your knuckles/away from you, it bunches up and wrinkles, thus making the area wider and expand in a way.
Your skin is made taut and is pulled back when you first enter a niche or small gap, making it very easy to slide in to as it’s less resistance. The skin is then wrinkled and bunched when you try to pull back out, which makes that portion of your body wider than when it first entered, thus making it very difficult if not impossible to get back out.
The joints between your bones can compress easily and distribute the force when you’re pushing the body part into a gap. However, pulling it out pulls at the closest or weakest joint, causing a lot more pain.
Also, the body part may swell due to blood pooling due to the constriction or inflammation if you injured the part when pushing it through the gap. This makes it much more difficult to pull the swollen body part out.
Think about where the force is being applied. Finger goes in, force on hand. Finger comes out, force on finger.
It’s most likely the skin thing everyone is talking about, but I also like to think it, in part also has to do with how the body is shaped.
In art, a common shape we see a lot and are tought to draw from is triangles, and that’s because our bodies like to come to a point!
Your hand comes to a point at the fingertips. Your face comes to a point at the nose (and the sides of your face tend to be flatter). The top of your head comes to a point from your shoulders.
If we’ve learned anything from moving objects around, it’s always easier to get an object from one spot to another, slimmer side first (as you’re able to get more of it in and then alter said angle to fit the rest through). It is far more difficult to get objects through fatter end first.
For example, you push your face between two bars of a stairwell. You struggle to get your head out. This is because the front of your face is the slimmest, the sides of your face tend to be the flattest (as well as force and skin making it a whole lot easier). The back of your head is round and isn’t flat like the rest of your face. It will struggle to get out back end first.
Your fingers form a point, you are able to push your hand through a whole and change their position to allow the rest of your hand inside. You struggle to get your hand out because it’s base is wider than the fingertips.
You can get through a hole head first, and shift yourself and arms around easily to fit your shoulders through. You’ll struggle to get back out because you tend to be wider at the shoulders than your head and therefore won’t be able to fit enough of yourself out to aid yourself more easily.
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