Final answer:
A bicycle braking involves direct physical contact and friction between the brake pads and the wheel or disc. So the correct option is B.
Step-by-step explanation:
Among the options provided, the force that is classified as a contact force is b. a bicycle braking. Contact forces arise from the direct physical interaction between two objects. When a bicycle brakes, the brake pads physically contact the wheel rim or the disc, creating friction, which is indeed a contact force. This frictional force slows down the bicycle.
Contact forces, such as the one experienced during bicycle braking, result from interatomic electric forces and include tension, friction, normal, spring, and buoyant forces. Therefore, of the options given, only bicycle braking involves direct contact between objects, which makes it a contact force as defined by Essential Knowledge 3.C.4 in physics.