Here's a more formal definition:
Friction is a force that opposes the relative motion or tendency of motion between two surfaces in contact.
Here are some key things to remember about friction:
* It always acts in the opposite direction of motion (or potential motion). For example, if you push a box across the floor, friction acts in the opposite direction, making it harder to push.
* It depends on the materials in contact. Rough surfaces have more friction than smooth surfaces.
* It can be beneficial or harmful. For example, friction allows us to walk without slipping, but it also causes wear and tear on moving parts.
Let me know if you want to learn more about different types of friction!