What is friction really? Is it just an accidental effect from the surfaces rubbing(?)? Does it occur when there’s movement only? How does the experiment bottle with rice helps us understand this?


Heck I’m confused right now. We do learn that friction is some sort of force that happens when surfaces sliding each other but doesn’t it sound like it’s just an effect? And is friction all bad? And need to be gone?

And the experiment we have to learn more doesn’t help much. I just understand that there’s less friction between the surfaces of rice but idk how it makes the pencil able to lift the bottle? Please help and thank you.

In: Physics

on a microscopic level, surfaces aren’t really smooth, there’s a bunch of little defects like ridges, bumps, depressions and so on. When two objects are touching and you try to move one, the little defects get caught on each other and try to stop the object from moving. This is friction. It’s not always bad though. Tires and brakes use friction to work and are designed to have increased friction. Friction keeps the tires stuck to the road and allows vehicles to move and turn. Similarly brakes use friction to slow down wheels, and therefore the vehicle (note that this requries tire friction as well).

I’m not super familiar with the bottle experiment and i’m going off a quick google so I might not have it quite right. Essentially what’s happening is the friction between the rice, pencil and bottle prevent any of them from slipping, allowing you to pick up the bottle with the pencil.

I’m not familiar with the rice bottle, but I’ll give it a try explaining, keeping it at least ELI10.

Imagine pushing a heavy box across a wooden floor. Both the box and the floor may look perfectly smooth to your eye.
It may **look** like this _______________________

But if you look really closely (down to microscopic levels) there will always be tiny little ridges/bumps in the material. So if you zoom in far enough,
Both the box and the floor will look more like this: ___/\__/\_/\_____/\___

These little bumps will “hook” into eachother as you push the box. That’s friction. Depending on the materials involved it may be very high (ex. a car tire on dry asphalt), or very low (f.ex. polished steel on glass)

Whether friction is good or bad depends on the situation.

* Sometimes high friction is good. F.ex. between your car’s tires and the road.
* Somedimes high friction is bad. If you run your car’s engine without oil friction will be high, causing it to wear out quicker.
* Sometimes low friction is good. Like between your ice skates and the ice.
* Sometimes low friction is bad, like if you walk across ice and you boots slip, causing you to fall.