To get the force required we first define the coefficient of rolling friction as the ratio between the resistance force between the surfaces in contact and the normal force due to the body.
Maximum static force = Coefficient of rolling friction x Normal force
Rolling friction was used in the calculation of the frictional force opposing the wheel rotation as the system is allowed to roll (to start the motion). The static coefficient of friction was not used in this case because it does not take into account the wheel’s ability to rotate, in the case of using the static coefficient of friction this will give use the force required to start moving the vehicle from rest while the brakes are applied, which is not the case here. The next two figures illustrate the difference between using the rolling coefficient of friction and static coefficient of friction. But this study of the difference is done on a normal bicycle with combined mass of 110 kg (driver and wheel) just to show the use of the rolling and static coefficient of friction.
Static coefficient of friction:
Assuming the brakes are applied and the weight is distributed evenly, therefore the force required to start the motion on the rear wheel is given by:
0.8 x (55 x 9.8)= 431.2 N (brakes are applied to prevent rotation as if it was a stationary object and a force is required to move it)
Rolling coefficient of friction:
This is the calculations required to start the motion of the wheel while it is allowed to rotate (no brakes are applied in this case).
0.0055 x (55 x 9.8)= 2.965 N (no brakes are applied, allowed to roll)
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