Starting a bicycle is harder than maintaining speed due to inertia. Newton's First Law, also known as the Law of Inertia, states that objects at rest stay at rest, and objects in motion stay in motion unless acted upon by an external force. This is why you must overcome the bicycle's inertia to get it moving.

Newton's Second Law explains how to overcome inertia: force equals mass times acceleration (F=ma). To accelerate, a force must be applied. More force leads to quicker acceleration, and greater mass requires more force for the same acceleration. Your legs pushing the pedals provide the force to accelerate the bicycle.

Newton's Third Law states that for every action, there is an equal and opposite reaction. When an object applies a force (action) on another, the second object applies an equal and opposite force (reaction) back. For a bicycle, as the wheels push backward against the Earth (action), the Earth pushes forward on the wheels (reaction), propelling the bicycle forward.