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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Bikes offload a lot of their convenience to the environment – without smooth asphalt pathways flattened by fossil fuel burning bulldozers they would be much less useful. Imagine taking [an early wooden bike](https://i.pinimg.com/originals/c0/08/0a/c0080a1d0fd9573dd75cc052c0b365d8.jpg) out to a national park to hike up a hill over the grass and off the trails. Then it would be you pushing the mass of the bike up a hill, harder work than just climbing on your feet. On the way down if the ground was too rough you couldn’t ride the bike you would have to walk it, fighting to control the bike so it didn’t drag you down or fall over. Lose lose both ways. Even on a modern mountain bike people generally ride trails of smoothed out terrain. Check [this video](https://youtu.be/rdNANaYbkfI?t=589) he’s struggling to push the bike and it’s flat, smooth, clear of rocks and tree roots and potholes and bushes and brambles and tufts and thickets, it’s not uphill, it’s only wet and muddy and that alone is enough to turn the bike into a burden.
Bikes benefit from precision engineering that biology can’t do – ball bearings, grease, axels, pneumatic tyres; animals don’t have wheels – there isn’t a good way to get nutrients and blood flow from a body to a completely disconnected wheel, and there isn’t much use for wheels in overgrown wilderness/swamp/jungle. These things and pavement combine to give bikes very low rolling resistance and the ability to coast forwards while not pedalling, compared to walking, and that works best in urban environments with flattened roads.
As well, bikes keep you level – turning the wheels only moves you forwards not up and down. With walking when you step forwards and [your legs move apart, your torso lowers](https://image.slidesharecdn.com/sehs4-161114192204/95/sehs-43-biomechanics-ii-433-force-com-20-638.jpg?cb=1479151341), then to bring your legs back together you have to lift your bodyweight a little bit. Some of your walking energy goes to continually lifting your body weight against gravity.
Other answers are saying that bikes have gears which give you mechanical advantage, which is true but it’s not relevant. Leverage lets you turn “I can’t move this lump it’s too heavy for my muscles” into “I can move half the lump, twice”. You put in half the force, for twice as long. Same total energy, levers don’t give you free extra energy.
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