Liquid is incompressible, so will carry the force applied at one end of the brake line through to the brake pad. At the same time the brake line maybe flexible.
It is not useful because if the liquid run out the car can't stop but if you use air than it is useful as when the air runs out there automatically comes more
Brakes are meant to have a lot of friction and it's useful.
Brakes, and Shoes
Wooden match and car brakes
The brakes! And the tires (no friction = no traction).
It is not useful at all for that. I use a proprietary brake cleaner from the auto store .
by turning it on :)
It is helpful for when you walk .
The friction is useful on a bike when you push it.
The liquid is called brake fluid. Sometimes it is called brake and clutch fluid. Both are the same.
Brakes are designed in such a way as to give off a loud squeel when they are coming to the end of their useful life. If your brakes are squeeling loudly and have been for a while it is a good idea to make plans to look at them.
It most likely means that your brakes are very hot, and that some sort of liquid has touched your brake pads or rotors. Be careful about warping in the rotor.