Physics plays a vital role in everything we do, whether we are aware of it or not. The sport of cycling is no exception to the physical laws of Mother Nature. Friction is a resistive force that always acts in a direction opposite to the movement of a body. Friction forces depend on two components; the coefficient of friction and the normal force. Friction = (μ)(n) There are two different types of friction coefficients, static and kinetic. The static friction coefficient is the friction force that must be overcome before any movement begins. It's caused by the tiny contact points between our tires and the riding surface (there are friction losses at every mechanical connection on the bike, but these won't be addressed within the scope of this article). The kinetic friction coefficient is the frictional force action when our bicycles are in motion. Like all frictional forces, kinetic friction acts in a direction that opposes motion. Normal force is simply the force exerted by the ground on the rider and bicycle. It is in turn equal and opposite to the force that the cyclist and the motorbike exert on the ground. This is in accordance with Newton's third law. Three main frictional forces affect a bicycle, friction between the tires and the riding surface, friction caused by braking, and wind resistance. There are other frictional forces acting on the bicycle, such as those found in bearings and other moving parts, however for the purposes of this article only the previously mentioned forces will be discussed. Frictional forces can also be found between the tires and the surface of the bicycle. the ground. The presence of friction between our tires and... the center of the paper......t rests. The second case occurs when the bicycle suddenly stops but due to their inertia the cyclist continues to remain in motion. Gravity is the force of attraction between objects and the center of the earth. It is always present and does its work for or against you. Gravity is the reason it's harder to ride a bike up a hill than down one. When you travel uphill, gravity works against you. It's a force that pulls you and your bike towards the center of the earth, opposite to your preferred direction. As you continue to travel up the hill, the force of gravity becomes stronger. Since Force = Mass x Gravity (Newton's second law), you need to apply more force to the pedals to compensate for the opposing force of gravity. On the way back down the hill gravity is still working on you and your bike, only now it's to your advantage.