At the contact between the rubber of the wheels and the road surface.
At the contact between the wheel rim and the brake pads.
It's useful on the tires, pedals, grips and saddle. and it's not useful in the bearings.
In some places it is, in some it isn't. Bearings for instance would do better entirely w/o friction. But handlebars would be really hard to hold on to if it wasn't for friction.
braking
Brakes are meant to have a lot of friction and it's useful.
The brakes! And the tires (no friction = no traction).
tension , compression and friction
There is friction between the rubber tires and the road or other riding surface.There resistance to the rider moving through the air.The bicycle's chain, pedals, gears, etc all develop frictional forces.
Friction Is Useful For Lots Of Things Like Walking Or Riding a Bike
In the bearings and in the tires. All it does there is turn into heat - and we can't use that for going forward.
Yes, because you don't inherit the skill of riding a bicycle.
you will be riding a bicycle
It gives you a nice, low-impact aerobic exercise, and allows you to travel useful distances w/o contributing to pollution.
I am not riding
A bicycle
That's all down to how hard you're riding. Most people will use more effort when riding IRL than riding stationary bikes.