1. Opposes motion: Friction always acts in the opposite direction of the object's motion or intended motion. This means it makes it harder to start moving an object, and it slows down objects that are already moving.

2. Generates heat: When two surfaces rub against each other, the friction between them converts some of the energy of motion into heat. This is why your hands get warm when you rub them together.

3. Wears down surfaces: Over time, the constant rubbing caused by friction can wear down the surfaces of objects. This is why tires wear out, and why you need to oil moving parts in machinery.