I understand that the bicycle stores potential and kinetic energy so for example when you go from the foot to the top of a hill and back, you have to only pedal for half of the trip. When walking you exert energy downhills too.
But what seems strange is that for small inclines you can still go very fast (compared to walking) and for a small effort.
What is stranger though is that on very big inclines (those that I have to select the lowest gear) it feels like I am exerting much much more energy than walking and I am going at the same speed as walking (sometimes I will dismount and walk the rest of the incline).
The friction is different. Try “coasting” mid-run and compare the distance you go then with the distance you go if you try coasting on a bike at the same speed.
Gearing. Or in other words, matching the impedance between the muscles and the load.
The human body is like a car with only the 1st gear. That’s why we can climb steep hills and stairs. But it’s not optimal for walking along a flat road, or even a slight uphill; your legs have to move so fast that you’re mostly expending energy to move your legs back and forth.
A bicycle gives your legs a higher gear ratio, so they can work at a more efficient cadence.
How does this work, physically? Work is defined as force X distance. Force in turn is mass times acceleration. The distance is the same, and the weight is slightly higher with a bike. Acceleration at first glance is higher on a bike, but since our ride and walk are both roughly a constant speed, we must be talking about the forces used to overcome friction to keep us at that constant speed.
Is it just that rolling friction is less than static friction? Is it pushing down on the pedals versus pushing forward off the ground? I think I agree it has something to do with the gears, torque and angular momentum, but I’m not sure exactly how that works.
The weight is irrelevant, or at least not directly relevant. Work isn’t just any old force times any old distance; it’s the dot product of force and distance, which means that forces perpendicular to the direction of motion make no difference at all, and forces that are close to perpendicular make only a small difference.
There is a good deal of vertical motion associated with traveling by foot, so you waste a lot of energy basically bouncing up and down, this is virtually eliminated on a bike. In addition a considerable amount of energy is wasted shifting your weight around, having to swing your foot/leg forward with every step, etc. Only about 20-25% of the energy expended by your feet against the road goes towards propelling you forward when running, whereas over 90% of the energy flowing from your feet to the pedals moves you forward on a bike.
Gearing matters, but the most important step is getting wheels. Then you get the benefits of coasting and of the forces you impart being more aligned with the direction of travel. The first bikes had no gearing, or even pedals, you just kicked along with your legs. They still beat walking on a level surface.
Are you sure that you’re cycling at walking speed? Could it be that while you are cycling at the lowest possible speed for that gear, you are still moving considerably faster than walking pace (typically around 2-3 km per hour if you are walking up a steep hill)?
In theory it should take less energy to cycle up the slope than to walk up it at the same speed.
I agree; you’re probably going faster than walking speed. You might just possibly be going at a brisk on-the-level walking speed, but if you tried walking up the hill that fast, you’d have to stop and rest, too.
Few bicycles are geared low enough to really go at an uphill, pushing-the-bike, walking speed.
Again, it depends on the gearing. On most bikes, even the lowest gear is higher than 1:1 gain ratio. (Gain ratio is the ratio between pedal movement and bike movement; 1:1 means the bike moves forward 1" for every 1" of pedal movement).
Bicycles are more efficient on certain types of terrain. Flat paved surfaces are ideal. But you can walk through a swamp more efficiently than you can ride a bike through it.
Beat me to it. Legs and feet sacrifice efficiency for the versatility of being able to traverse uneven surfaces as well as climb, jump, and balance.
Think about it. The bicycle wins the race on flat pavement but would lose the race climbing a hill of 3 feet wide boulders. And it would fail miserably at tree climbing.
It is a set of simple machines that improve efficiency only under special conditions.
Pedal 10 strokes on a bike. Then stop. You keep going for a while. That’s using more of the energy you produced.
Now walk 10 steps, then stop. You just stop.
The wheel uses more of the energy to produce motion than your legs can. Even while you’re pedaling, not just coasting, the wheel gets you further per stroke and doesn’t waste momentum when you stop moving your legs.
This is the real answer. When you walk, you are actually pushing yourself up and forward. One foot stays flat on the ground, the other pushed upward so that your body pivots on (mainly) your ankle. you then have to swing the other leg forward to stop that pivot. Repeat now, pivot on the other leg now forward.
The amount of work required (and efficiency) is obvious by trying to walk with exagerratedly long strides. It takes a lot of enegry to push your body up and forward with one leg if your other leg is too far forward.
(By constrast, running is jumping from foot to foot, in longer strides but they are still small arcs.)
Additionally, there the muscle actions involved in keeping balance.
With a bicycle, there are assorted secondary effects, such as creating rotational momentum in the wheels - but essentially, you raise your body then gravity turns a crank, converting that high into low and kintetic energy using a crank, essentially a form of lever. On smooth, solid surface the friction due to rolling resistance is very low. So you can coast on that work until friction slows you down.
(Allegedly your legs are very strong usually, and can lift more than your body weight - so a reclining bike is far more efficient. Instead of lifting only your body weight and letting gravity do the work, you are doing leg presses on the pedals with your butt pushing against the back of the seat. Most people can spend more effort this way.)
In both cases, walking and cycling, going up takes more energy as you convert kintetic enrgy to potential - your position higher in the gravity well.
Consider if you walk downhill, you have to expend muscle effort (energy) just to stop yourself from running away on a steep downhill.