Recently I turned 18, and with that comes extra driving priveleges for those who did not take drivers ed. Thinking about all the years of being a kid made me ponder a time before I ever drove a car, when I would ride my bicycle. I can remember when I was younger riding my bike almost every day during the summer - wind blowing through my hair ready to go up to the high school's turf. Pondering this thought again now, there are a lot of physics applications in cycling.
The bicycle takes power from us and converts it into kinetic energy by turning the wheels with an angular velocity. In addition, the bicycle is very efficient, converting 90% of the mechanical energy applied by the user into kinetic energy. Interestingly enough, automobiles only convert about 25%. Also, when you hit the brakes this kinetic energy is converted into heat energy since the force of friction causes the bicycle to slow down significantly (lower KE), depending on how hard you brake. Of course air resistance comes into play as well, increasing in force as you increase your speed. For a racing bike on a paved road, about 80% of the work done is to overcome air resistance, and the other 20% is to overcome what is called rolling resistance (higher the load, higher the rolling resistance). For very serious bicyclists, handlebars are looked at when considering air resistance. Handlebars that are wider provide more torque to the user (since we know Torque = FLsinθ). This is why bicyclists will have handlebars that are closer together than usual handlebars, to keep their arms in close so there is less resistance. This is also why they tuck their head down and wear aerodynamic helmets.
Overall I'm glad that I don't have to ride my bike as much as I did before. If I were to now though, at least I would understand what i'm doing!