ELI5, How am I able to go farther and faster on my bicycle than by walking, considering I have to move the mass of the bike, as well as the loss of energy to friction from the gears and wheels?
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The energy required to move you and the bike versus energy transfered from you to the bike is not 1 to 1 thanks to the transmission and wheels. It’s no different in cars. How can a 1 liter engine move a 1 ton car? It’s the transmission that makes it possible. More gears means more of the energy is efficiently transferred to the wheels. Same applies to bicycles: we are the engines and the gears and chain are the transmissions. Granted, there are bikes with a single speed; however, they typically come with oversized tires and cranks to offset it.
Assuming you have a hard, smooth and flat surface – *it will preserve your momentum.* By taking a bike away from those conditions then it may be less efficient.
The hard and smooth part is important. If you take something like a road bike and try to ride through sand, snow, very rough terrain, etc… it will have much more energy loss from sinking into the ground, pushing material away, or just bumping into things. This is often less efficient than walking not even due to the weight, but sort of analogous to “dragging your feet”.
However, there are plenty of specialized bikes to handle many obstacles. The biggest advantages for various terrains will be really big tires to reduce sinking into soft stuff and suspension to absorb bumps (big and small). This will significantly add to the extra weight and energy required to use the bike, *but it will preserve that energy in many more conditions.*
Assuming you’re not being bogged down somehow by the ground, the rolling friction is very small. You’ll actually be held back much more by air resistance. Combining that with the fact that you can coast with 0 spent energy downhill and use gears to best utilize your output and it really becomes quite efficient.
Several factors come in to play here. First is the ability of a bicycle (free-spinning wheels in general) to take advantage of inertia far more efficiently than you can walking. With walking, the moment your feet stop moving you stop moving, whereas the rolling wheels will keep you moving in the same direction without additional energy expenditure. The same is true of roller-blades or skates. Though they use similar motions to walking, they are much more efficient.
Another factor is body weight. With every walking step, you have to lift and support your entire body weight on your legs. On a bicycle, most of your weight is “comfortably” rested on the bike, and you only need to lift the weight of your legs.
Additionally, almost all of the energy you put into a bicycle goes into moving it forward (This includes lifting your legs if you use clips or clip-less pedals). With walking, the only energy productively moving you forward is energy used to push off the ground. Energy to bring your legs forward and catch you from falling is essentially wasted.
Walking you need to keep outputting effort or you stop. A bike you can coast. With one unit of foot motion you move that same one unit. On a bike that one unit could be much farther. To run the speed of a bike you also have to reset your legs; it takes energy to swing each leg forward fast enough.
That’s the point of machines, to make our energy output more useful.
Waking while carrying the bike or rolling it next to you will take more effort than just walking.
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