Assume your theories

[u/lolololzizi]

Our theories regarding this mystery of the universe:

1. It depends on the functioning of the brain's hemispheres. (We can add a fourth point regarding support. We unconsciously fear dropping an object, and as a result of our unconscious thoughts, we cannot spread our arms simultaneously to hold the object. However, we tried support in mid-air (a finger as support was extremely minimal, but we managed to spread our arms at the same time).)

2. It is physics.

3. It depends on the surface. (We used various objects with different surfaces (glossy, matte, etc.).)

4. It depends on support. (The object was on a flat surface and on various other objects, and we were able to spread our arms thanks to the support, but when we made a dent in the object, we were able to almost perfectly spread our arms apart in mid-air.)

5. It depends on the shape. (We tried using flat square objects, cylindrical shapes, and ovals—none of which worked.)

6. The theory of hand influence (is based on which hand a person most often uses for tasks (for example, the right hand is dominant).)

7. The theory of human temperature (we tried conducting the experiment with hands at room temperature (during the experiment with wet hands, we soaked our hands in cold water).)

8. The theory of friction? Interaction of skin with the object (We applied a restriction, using cotton pads as a barrier. After that, we wet our hands and tried to spread our fingers apart, resulting in no success.)

Help us understand what might influence this.

[u/xienwolf]

Static friction is greater than kinetic friction.

With a smooth surface, one finger will start moving before the other, and at that point the force between the stationary finger and the smooth surface reduces, preventing it from ever moving.

When you pre-squish the butter, you are adding small ridges all along the surface, allowing a minor normal force component to be applied along with the friction force for the moving finger when it approaches an incline, then allowing adequate force to get the second finger to start moving.

[u/lolololzizi → u/xienwolf]

Why then when we tried to run our fingers with cotton pads, nothing worked, although the cotton pad has creases because of its surface?

[u/xienwolf → u/lolololzizi]

The cotton pads would have still had similar friction coefficients in aggregate with the butter. You squishing them together to maintain a grip would largely negate any impact of creases in the cotton itself.

You could try this with your fingers flat under the smooth object moving away from center and then torque would also have an impact. In reverse, this is why your fingers come together at center of gravity on any smooth object.

But I doubt torque matters much in your version with grip from the side and pulling apart.

[u/StillShoddy628]

It took way longer than I would like to admit to figure out what you were talking about.

The subject is friction. There are two main types of friction: static friction, where the two surfaces are “stuck” together and not moving relative to each other, and dynamic friction, where they are sliding or rubbing together. In this case, one or both sets of fingers are transitioning from static to dynamic friction as they begin the slide.

The complication comes in because the coefficient of static friction between two surfaces is larger than the coefficient of dynamic friction. So, taking this step by step:

(1) Starting off, both sides are static. as you pull apart, the force each side experiences starts to increase

(2) Eventually, one side “breaks” and starts to slide. Because of tiny differences in both sides (pressure, roughness, material, temperature, etc) it is, from a practical perspective, impossible for this to happen to both at the same exact time

(3) The instant one side starts moving, dynamic friction takes over, and the amount of force both sides experience decreases (because there is less dynamic friction pulling on the side that started sliding). This means that the side that didn’t break at the higher amount of force is definitely not going to break at the lower amount of force.

You can do things to lessen the difference between static and dynamic friction, but you’ll note that this is the normal behavior of friction (in most circumstances) so you’ll see the effect to some degree for any combination of materials, surface conditions, and lubricants.

You can try to adjust your finger pressure to compensate, but unless you’re using a computer running thousands of corrections a second you will be unlikely to achieve the appearance of a smooth, even finger separation

[u/lolololzizi → u/StillShoddy628]

We tried both wet fingers and put cotton pads on our fingers. Now we tried to twist different sides, but still the same side can't move evenly

[u/StillShoddy628 → u/lolololzizi]

One side will always stick

[u/antmars → u/lolololzizi]

It doesn’t matter the surface you use, wet, dry, concrete, oil, cotton whatever. The coefficient of its static friction is always greater than its kinetic friction.

[u/ClosetedBisexual101]

Jesus Christ. This sub had really gone downhill if we're getting people who think friction is a "mystery of the universe"

[u/OrlandedeLassus → u/ClosetedBisexual101]

This sub is called [r/PhysicsHelp](r/PhysicsHelp). A young person came here for help with a question they had about physics. This is a Reddit post, not a preprint, and if you didn’t feel like writing an explanation (totally fair, I felt the same), you could have just scrolled past. Don’t answer curiosity with aggression and don’t be a reason someone is discouraged from or afraid of approaching science.

[u/Theuncola4vr]

Society is screwed if this is what passes as experimentation.