Name two ways that friction is harmful and two ways that friction is helpful to you when riding a bicycle

Harmful-causes heat; if it's not used correctly, it can cause injury-when falling, the friction between your knee/leg and the ground can cause scrapesHelpful-helps stop the bike, the brakes rub against the tire which slows it down to a stop-it can also help move the bike; the chains rub against tires which accelerate the bike