When do you need friction?

Answer 1

You can't say for definite but in general, 2 very lumpy, rough surfaces rubbed really hard against each other would create the most friction.

Answer 2

so you could slow down a car or write with a pencil
in walking

for nailing

for braking

for slowing down something that is rolling

Answer 3

When one object rolls over another object, like when the wheel of a car rolls over the ground.

Answer 4

when braking