It has to do with gravitational pull.
If you're rolling downhill - gravity. If you're going along on the flat - the pedalling effort of the rider.
In the simplest of explanations, they are downshifting. It makes it easier on the legs, as it requires less energy to push the pedals, but also the causes a lower ratio of turns of the pedal to turns of the wheel.
If mud slides downhill, then yes, gravity makes the sliding downhill happen.
The basic reason is going to be friction. The brake pads rub against the tire or tire rim to create it.
The salt,cold or sand
rephrase... question makes no sense
The pedals, crank, chain, sprockets, and wheels. Along with the rider, they all work together to make the bicycle go.
A compound machineA bicycle consists of several simple machines, which makes it a complex machine.
A bicycle consist of several simple machines, which makes it a complex machine.
Friction and pressure.
kinetic energy
The front of the car is blunt, making it easier to 'cut' through air, thus reducing friction. For a bicycle, since it is very thin and angular, its shape (and the tires') makes it easier for air to glide over the bicycle, thus reducing friction.